Hyrdration, hyrdation, hydration up to a couple of hours
If it's warmer / faster then some weak energy drink, and a stash of a couple of power bar gels in case.
On a longer ride (chance would be a fine thing) something to nibble on the way. Mars bars, flapjack etc.
Of course, post-ride snacks are the best. Chocolate cake, taken with tea and your favourite bike magazine in the bath. Bliss!