+1 on M102404's list, especially the baby wipes.
Make sure that the T- shirt under your BDU's is poly pro. It'll trap heat next to your body wich will keep you warm when it's cold and make you sweat and cool you down when it's hot. They dry super fast as well, not like cotton t shirts.
Also plan around what your group will bring so you don't end up bringing duplicates on the field. Not everyone needs to bring a way to boil water, or not everyone needs a tool kit. A few per group will do.