I take oil in nalgene bottles as well.  I haven't got anything to add regarding oil.  However, I'd like to suggest taking some aluminum foil as well.  Oven baked/steamed fish is a nice change of pace from frying.  Place filet on foil. Add a little margarine.  Some spices/herbs if you have them.  Seal the foil closed.  Heat on the coals or fire grate, ten minutes to a side.