I eventually want to give players little booklets specific to their class. Not brand new players, and maybe it could wait until 2nd or 3rd level, but I want them to know their options. So MUs would have info on copying spells, material components, and magic research. For fighters I wasn't sure what I'd put, though. Other than splintering shields and maybe some fighting orders they can join, there isn't much fighters know outside of combat.
So here are some ideas of bits of knowledge fighters might bring to an adventure party. This assumes a first level fighter isn't a bumpkin straight from the village, they at least participated in some raids, some hunting parties, and battles (or you could just hold off and give these to players at a higher level):
Hone a Weapon - You know your weapons. Spend one night in camp, no healing or watches, and you can ready a non-fighter's weapon to perfection. This means sharpening blades, fixing grips, even whittling staves to improve balance. This will give the owner a non-magical +1 while using that weapon for one battle.
Quiet Armor - You've had some experience with stealthy assaults. Spend one night in camp, no healing or watches, and using rags and a little lantern oil you can make one suit of metal armor as quiet as leather. Lasts one battle or one day whichever comes first.
Experienced Packer - You've spent time traveling with gear. Spend an hour and you can rearrange someone else's pack to hold a bit more (another line for simple encumbrance, or ~10 pounds) with no added effect on their movement. This lasts until they add or remove something from their pack.
Hunter's Stew - You know how to cook one type of game excellently. If you cook it, everyone that eats in camp will heal an extra hit point that night. Only works two nights in a row.
Defensible Camp - You know a good place to set up camp when you see it. Once a week you find one that makes your party less likely to be surprised and more likely to gain initiative if attacked (+1.+1).
Rouse a Comrade - You've been in hard fights before. When someone is knocked unconscious in combat you can take a round to get them on their feet and moving toward safety (pcs at 0 will be raised to one hit point). You can only do this for them once a battle.