With the ratios above, one donkey can carry 24 days worth of food, whereas one draft horse can carry 16 and 2/3rds days of food, which means that for a dungeon three days away, you will want at least one feed donkey per eight donkeys (including himself), but one feed draft horse to every five draft horses, give or take.
Wagons will generally take up a fourth of the gross pulled weight. Thus, a one-horse wagon weighs 300lbs and has a payload of 900lbs. Sledges count double for encumbrance, except over ice and snow (and special desert sledges over sand, if they exist in your game).
Renting a beast costs %1 of purchase price per week, a number I pulled out of thin air, probably with a deposit. A wagon costs roughly $100/200lbs of cargo space, cheaper for ox-carts, more expensive for more exotic wagons (like an elephant-wain), and probably rents for roughly %0.5 of purchase price per week, or a %5 one-time fee, which are also random feel-good numbers.
Travel ratesA mixed party of people on foot, on horseback, and/or with a wagon will move at the regular hiking rates on B351, but with no chance to get the extra %20 for Hiking skill (but see below). This assumes 10 hours of movement at Move MPH and 2 hours on each side for starting and stopping. (If the party wants to go longer, see Extra Effort, below.) Any combat or other similar encounter will take roughly an hour to resolve, what with stripping the bodies, getting the horses calmed and moving again, etc. Alternatively, while it may not take an hour to get on the road again, people probably stop earlier in the day due to fatigue. Season to taste.
Terrain, weather and wagonsAny terrain worse than "Bad" or any weather worse than ankle-deep snow will stop a wagon. Generally, any combination of factors that would reduce movement by more than half is impassible to wagons. Specifically, mountains and bogs are impassible, unless there's a road, which overrides terrain quality as per B351, and will probably take a very circuitous route.
Terrain, weather and animalsPonies and mules are commonly known* to be better at picking their routes in bad terrain than horses. Specifically, people bring mules and ponies into bogs or over mountains, not horses. To simulate this, optionally give ponies and mules a +4 to skill rolls for travel to offset penalties due to terrain. (See below.)
Camels and donkeys/mules are commonly known* to do better in deserts than other animals. To simulate this, optionally give camels and mules a +4 to skill roles for travel to offset penalties due to terrain. Also, camels count as having snowshoes for reducing movement rate modifiers (sand and snow are never more than ankle-deep, which reduces movement by a factor of 2).
Skills and their uses
Hiking: As per the Basic Set. However, remember that the slowest member of a party determines overland speed, unless people want to separate. Assign penalties due to terrain up to -5 (for very difficult terrain, like the Himalayas). (Otherwise assume a simple failure and 100% land-speed.) Any critical failure is a hiking mishap of some kind - turned ankle, blisters, extra marching because the map was read wrong, etc. Assess 1d6 injury and 1d6 fatigue loss to a random hiker.
Packing: Rather than a caravan moving at %80 if it doesn't have a packer with skill 15+, the person with the highest Packing skill rolls daily. Success grants +10% movement; success by 5 grants +25% movement. Alternatively, each +1 the roll was made by grants +5% movement. Any failure by 5 or more results in some baggage mishap - lost cargo from poor knots, a hurt animal due to chafing, etc. Any critical failure means catastrophe - an animal broke a leg or sank into a swamp, or multiple beasts lost their baggage in a river, etc. Assign up to -10 due to terrain - it's more difficult to get horses over the Himalayas than people.
Riding: If people are on horseback, treat Riding like Hiking above. If a critical failure is rolled, assign fatigue and injury both to a random rider and his horse.
Teamster: You only need this skill if you have a wagon. If you only have a wagon and no beasts of burden, you only need this; else, you need both this skill and Packing (see above). This skill doesn't provide any benefit - it's a skill tax for using a wagon. Roll once a day. Failure means driving the wagon takes 1-3 hours longer than it otherwise would - players may choose to stop early or push on to make up lost time. Critical failure behaves as described in the skill on B225. In addition, there is a 1 in 6 chance of lost baggage - around half of that in the wagon in the first place. (You decided to ford the river instead of caulking the wagon and floating it.)
FatigueMoving overland is fatiguing. At the end of the hike each night, assess 3 hours worth of hiking fatigue as per B426. Halve this if the person has the Fit advantage; quarter it for Very Fit Yes, this means that your average ST 10 human will take 9FP from hiking in temperate weather. (Remember fatigue from weather and wearing armor, as well.) Don't add any fatigue assessed because they stopped in the middle of the journey to do something else (see B426), unless that fatigue should last (e.g. fatigue from illness). Any fatigue in excess of available FP comes off as injury - yes, you can kill yourself hiking.
Extra Effort: Rather than a flat 2 FP at the end of the day, Extra Effort costs 1 FP per +%5 distance covered. You can also use this with Packing, Riding, or Teamster, substituting a contest of wills between the beast with the strongest will and the designated driver/packer instead of minuses to the Will Roll. Yes, you can kill your horses this way.
Water: These rules assume the terrain you are travelling through will have sufficient water, so all you need to bring is foodstuffs. If this is not the case, animals also need a half-gallon of water per 100 lbs per day at 4 lbs per half-gallon. (Water's free, except at desert wells.) Camels can go without water for two weeks, and then begin to suffer fatigue and injury (see B426) at half the listed rate. Also, treat the listed amounts on that page as units to be multiplied by water requirements rather than absolute values.
Running out of food: If the party doesn't have enough food to keep the pack animals fed, the animals can forage to offset the difference. (It's up to you as GM to determine how well this works for omnivores or carnivores.) See B427. However, ruminants take a long time to get fed; slash travel distances in half in good, grass-filled terrain for horses and the like. Oxen and elephants will need to spend all day eating. If the terrain is less favorable to rumination (swamps, high mountains), multiply the time taken by 1.5-2, or more for especially bleak places. With little enough grass, the party is better off stashing their spoils, butchering the horses, and hiking to civilization to procure more supplies. Camels can go without food for a month, and then begin to suffer fatigue and injury at half the listed rate.
These rules are very simplified, and probably wrong as far as realism is concerned. I wanted something I could use to decide quickly how long it would take to move from place to place, and a system that involved meaningful choices for the players, not a dissertation on the vicissitudes of low-tech travel.
This system does not sync up well with the stats for the wagon in the Basic Set, of which I could make neither heads nor tails, given what I understand about how much a horse can carry vs. its ST in GURPS terms. In all cases I have assumed that a horse is capable of carrying heavy encumbrance for a workday, which is convenient because a) it doesn't slow people down and b) it passes the sniff test for me, since horses will refuse to carry too much weight in my extremely-limited experience.
Further, my hiking rules are different from those in High Tech, which calls for a movement speed equal to Move/2 miles per hour. That book also claims that the rules in the Basic Set involve 16 hours of hiking at this pace, which is patently absurd; ideal terrain and no encumbrance involves hiking Move x 10 miles, which at a speed of Move/2 MPH, would be 20 hours of hiking.** So, instead, I came at the problem from two different angles; first, ten hours of actual movement, eight hours of sleep, and four hours to break camp, eat, make camp, etc. made sense to me for people who aren't hustling. Second, I went to the Vehicle rules and found the canonical ruling that speed in mph = 2×move, and that Cruising Speed for vehicles was usually %60-%70 Top Speed. I moved that down to %50 for ease of calculation and rationalized it away.
Pull loads were achieved by the formula given in the table, BL×15. This comes from B353. My sources (below) said that a horse can pull a draft of one-tenth its body-weight for eight hours a day regularly, and that a wagon's draft is somewhere between %10-6, which was a nice confluence, since if that rule didn't exist, the rules for carts would allow you to move a truly absurd amount of stuff. In particular, the rule that a four-wheeled conveyance divides encumbrance weight by 20 fails the realism test, hard.
Camels I eyeballed. The Basic Set gives them Reduced Consumption 3, whereas Wikipedia claims that dromedary camels can, in a pinch, go six months without water and other sources say 1 week to a month without food. However, when given the chance, they'll eat and drink enough to make up the difference.
Generally, these rules are designed to be easy to play while passing the plausibility test for a bunch of guys with little to no professional experience.
Care and feeding: Horse Sense by S. E. Mortimer, an excellent Pyramid Article that also happens to be a free sample, run quickly by GURPS Low-Tech Companion 3: Daily Life and Economics for agreement(ish)
Wagon drafts and horse loads: Tiller International: Estimating Wagon Draft and Wagon Teamster, a guy who decided to sell his house, buy an RV and some horses, convert the RV into a horse-drawn carriage, and travel the United States.
Stats: B459-60, though I checked against Animalia in GURPS as well.
*By us armchair philosophers, at any rate.
**Should I submit an erratum, perhaps?