I drink Diet Pepsi, tea, coffee, or energy drinks(if I'm REALLY in the mood). They're all generally clean and can be quickly sipped between waves of enemies, quests, and whatnot.
As for snacks? If I get hungry, I'll usually make a sammich or a bowl of cereal. Occasionally I'll eat chips or something of the sort, but that's when I play DS or handhelds, and I really hate greasy buttons. I'm okay with keyboards and mouses, my hand can stay gripped on that, but when I've got buttons and control sticks on consoles and handhelds, it just becomes a hassle.