Diet Coke is what fuels me through everything in my life, so obviously gaming is no exception. I've been known to get through three of the 2-litre bottles in a particularly thirsty day, though obviously I don't normally go for quite that excess.
I went through a brief phase of drinking a lot of Lidl's cheap knock-off version of Red Bull (exactly the same, 1/5th of the price) which I'd buy in cases of 24, often getting through ten cans in a session... and then wonder why I wasn't sleeping.
As far as food goes, well, y'can't really go wrong with biscuits. Digestives, fruit shortcakes, it's all perfectly acceptable as a meal when you're a student.