Hey, I can't believe this thread stayed on topic for about 60 posts. I think that's a new record.

Anyway, here I go:

Ketchup (Ketchup, Catsup, Ketchup, Catsup...) - in or out, doesn't matter
Maple Syrup - you're supposed to refridgerate it after opening. syrup can go bad
Mayo - uh...fridge
Milk - I like a nice, curdled milk, so...radiator.

I can't think of anything else...