Costco! I come here once in a while at lunchtime to grab the $1.50 hot dog and pop. Awesome deal! The hot dogs are big and juicy, but the toppings are limited. Big enough to fill you up and then you can wander around Costco drinking your pop...and eating the free samples for dessert! Haha.
The french fries are an option for a side, but they're just OK. They're of the reconstituted weird crispy (battered?) outside variety: think like KFC, but larger. The poutine can be pretty awesome, but when is it not? The cheese curds don't always melt though (gravy not hot enough?) Soft serve ice cream in a waffle cone for $2 is a nice dessert or snack after a shopping trip too.
They also have pizza and sandwiches, but I've never found either of these that enticing/tasty. The pop selection also recently switched from Coke to Pepsi (boo), but what can you do?
In terms of the store itself: be careful that buying in bulk is actually cheaper for you and that you actually want things in that volume (I'll often get tired of whatever it is I've bought before I finish the bag/box/whatever). Also, if it's clothes or the kind of product they'll only get seasonally make sure you grab it while you can because they're often gone by the time you go back...