The answer depends on a few factors, like what sort of tools are going to be maintained and what steel are we talking about. I used to carry a chunk of black and white compound and just apply it to any smooth bark or straight stretch of wood. Later I did the same with my walking stick when backpacking with a machete, just strop away every couple of uses. On softer carbon or stainless steels this strategy works pretty well, not so much on harder steels.
I don't normally bring any extra sharpening gear, but something like a combination silicon carbide puck is very handy. Slips into a pocket and can do pretty much any sharpening chore on any sized tool from pocket knife to axe, also work OK with water or dry for short bursts. Couple it with a block of compound used as described above, and you're very well prepared.
One of the things I take into account is that in most cases when on foot, there won't be anywhere stable to set a stone for sharpening - whatever it is, handheld is a big help, and being familiar with that style of sharpening equally so. I have a few 1"x10" Washboards that work great in this capacity on smaller blades as well as larger ones when held like a file, but haven't taken them packing yet. I don't generally need to touch up my knives during a 2-4 day hike, so all I'd use it for is to sharpen other folks super cheap, super dull knives, I'd rather collect firewood and drink a beer...