I was just there 2 weeks ago volunteering... (Score 1)

Lots of water & gatorade. You will go through it fast. A camelback type carrier (that holds at least 2 liters) is nice so you don't have to tote around lots of water bottles while working. Freeze some of your stuff before you come if you want anything even remotely cold (on breaks) while there. Bring energy bar type snacks. Food that doesn't require keeping cold or much prep. MREs are best (w/heater) if you can manage it. Dehydrated meals sound nice, but it is not easy to heat the water for them while out on the job. Sturdy boots (waterproof if possible in case you are mucking out houses). Good socks. Lightweight but protective shirts and pants. You will get tree sap all over them, so keep that in mind. You will also want something comfortable (and clean) to put on after working (shorts, etc.). Sturdy leather gloves! If your gloves are sketchy, buy some new ones. It is HOT and humid, so keep that in mind when picking your sleeping gear. Tent (w/rain fly) and a cot. Cots are a pain to bring, but you will be glad you have it. Put your misc stuff in one of those big plastic containers for easy carrying around. Backpack for meals and stuff while out doing work orders. Flashlight. Mosquitos might be a problem, although we didn't see many (thankfully!).

It was VERY hard work, but awesome to do. Enjoy!