You could go 3 days without washing your hair.. depending on how fast your hair starts to look greasy or just gross.
However if you choose to wash your hair at the camp, you could just pull it into a ponytail. Or just let it dry natural. If you really insist on having nice straight hair.. consider putting some some product that may calm your hair down a bit. (I would suggest trying this at home before you go on your trip, to see how it looks and if you like it.) (also, sorry I don't have specific names of products for you)
I hope i helped!! good luck sweetie.