We do our main shop every fortnight, and then top up on the essentials as an when needed. A lot of the fresh vegetables we buy are for my guinea pigs, so get used everyday, and our tomatoes get finished quickly too because my dad has them in his sandwiches for work. Otherwise we tend to buy frozen veg.
We always buy a lot of fresh fruit, but tend to stick with the stuff that will last longer - apples, oranges, pineapple - as opposed to soft plums and peaches which go off in no time. We also buy loads of bananas, but get them while they are still a bit green.
I hate wasting food, so even when our fresh food is past its use by date, I'll still chance it.