read this somewhere...tried it. it was QUITE effective.

If you cook a meal that has some grease/fat over a WOOD fire, you have everything you need to clean up.

Add a bit of water (hotter is better) and some of the ash from your fire to the pan. Tada! You have basically begun to make lye soap in the pan. Scrub it out with some pine needles. The solution/paste can be rather harsh, so be sure to rinse your hands well.

Be sure you use water that is safe to drink.
Hotter the water the better
Harder woods are better than softer woods.
You can help heat up the paste/solution by tossing in a chunk of hot charcoal
When the charcoal cools you can use it to scrub the pan