I take a 60ml nalgene jar with olive oil (60g). Enough to fry a couple of fish. If I'm lucky enough to catch more than that, well, its their lucky day, back to the creek they go.
Dehead and gut your fish and dispose of it in the creek. I assume I don't need to tell you why to do it this way.
I do not fillet the fish, but butterfly them in the pan. Cook on low heat, covered. Dispose of the bones and skin in the same place, well away from your campsite.
Another method of cooking, although I have not tried this, is to place some stones in the bottom of your pan, with the fish on top, cover and cook on low heat - almost like baking it. Put a little water in the pan so you don't scorch the bottom of the pan. A little bit of foil between the fish and the stones is ideal.
If your stove won't simmer, well that's another issue.

In light of the following post by billk the method I've suggested of disposing of entrails may not be an accepted or appropriate in some areas. You should first check with local govenment agencies for restriction that may apply to the disposal of entrails in the area you are fishing.