You can make a fire packet:
On a big piece of foil (1 ft x I ft) place potatoes, onions, bell peppers, garlic, pepper, your meat of choice (raw), and other veggies or ingredients that you see fit. Drizzle olive oil over the whole thing and wrap it up securely. I wrap mine with a second piece of foil. Then I place them in a big zip-lock bag and take them up with me. When your fire has been going for a while, you can just place the package (minus the plastic bag, of course) in a place with embers but not a bunch of flames. Turn it a couple of times, and let it cook for about a half hour. You might want to pull it out and check it at that point and you might need to throw it back in. Just use your discretion there.
Unless you have some camping pots or kettles with a secure lid, it'll be hard to cook coffee or boil water over the fire. I used to do that a long time ago and I ended up with ashy food. Seriously, a decent camping stove is $30 at an outdoors store and it is well worth the investment.
I use a Nalgene (or similar bottle-as long as it has a wide opening) and crack enough eggs for every one, put some milk and a chunk of butter in it. That way you can place the bottle in the river (or however you keep perishables cool) and it will last you the trip. Of course I cook over a camping stove. It's not healthy, but you should splurge and get a jiffy pop (http://en.wikipedia.org/wiki/Jiffy_Pop). It's fun and works over a campfire.
If you can't afford a camping stove, then take up things that don't require cooking such as pop-tarts, clif bars, jerky, trail mix, fruit, etc. The fire packets are awesome and don't require a stove, hot dogs, jiffy pop, marshmallows, will be good. If you can find a way to boil water without getting ash in it, then you can do more such as cook pasta or burgers.
I also bring hummus and tortillas. And pesto sauce.
Anyway, good luck and have fun!
