I know there will be water and other snacks around, and maps to check, but it's nice to be able to take stuff with (and to glug water in large quantities when I choose, which isn't feasible with the little cups that tend to be put out).

No eruv => no carrying, nothing in pockets (well, I don't think anyone is hyper about getting lint out of pockets...). Anything you wear is ok. Anything else, not.