Groceries make sense but you have to be careful. On the one hand, having sufficient groceries at home might prevent you from being tempted by snacks when you're out. But on the other hand, people can go crazy buying all sorts of convenience foods at the grocery store with the excuse that it's cheaper than a vending machine.
On the third hand, I like to not count groceries when I'm doing no-spend days/weeks/etc. because it will seem dire, that I need groceries like whoa, but then if I don't buy groceries somehow I manage to survive another week. I take advantage of free food events, I eat some leftovers, then I move on to the tremendous amount of pasta and canned stuff and freezer stuff stashed away.