You shouldn't have to worry about anything except for the damsel. They will have enough to graze and eat for your vacation. The Damsel should be alright, but it is iffy. If you don't want to risk it, there are a couple easy options. First, you can get an automatic feeder from just about any LFS
for $20 or less for a cheap model, or you could have a friend/neighbor just drop food in even once halfway through the trip to ensure the survival of your fish. To be honest though, he should be fine. If he gets desperate, he may pick at your snails in an attempt to get something to eat, but everything should live.