My kit is very simple:

20 ibuprofen tablets, 200mg
2 sterile gauze pads, 2x2 inches
5 band-aids, 3/4-inch wide
2 xlarge band-aids, 1-1/4 inch wide
neosporin anti-bacterial ointment, small tube
roll of adhesive tape (cloth-backed, not paper)
needle (stuck in cardboard) for blisters
3 povodine iodine wipes

To these I add some items I personally need:

Claritin tablets (allergy relief)
Benedryl capsules (allergy relief and sleep aid)
Phenylephrine tablets (decongestant)

I would love to have some wide-spectrum antibiotics and a few heavy-hitting painkillers in there, too, but I don't have any easy way to access these.

It appears to me that backcountry medical problems divide into two broad categories:

1) minor aches, blisters, burns, scrapes, bruises, scratches, cuts, or gastro-intestinal distress.
2) major injuries such as broken bones, internal injuries, gashes, concussions and the like.

My kit concentrates on the first category. Dealing with major traumatic injury will have to be a matter of improvisation with the materials at hand. Even if I carried a major medical first aid kit, I know my meager training would render it mostly dead weight anyway.