If you like Tostitos/Tortilla Chips, stock up. They are impossible to find fresh here, or are usually out of stock and they cost an arm and a leg.
Also, Ketchup Chips, they don't have em here. I'm not even sure if they have them in the US, it might be a Canadian thing, but they're pretty tasty.
Anything and everything for the bathroom.
If you play sports, stock up on athletic tape, mouthguards, clothing etc.