If you go there by foot or by bike, it means you cannot buy much.
While that's true it's not a big issue for me: I've got a back pack with two strong reusable bags to carry quite a lot. Usually I don't need them all. Fully loaded I've got to walk about 5 to 10 minutes back. If you have more there's always the option to use a shopping bag with wheels.
Therefore you need to go much more often and that you'll rarely buy any heavy goods.
Usually I go once a week. If you have heavy goods there's the option to use a car from the car sharing pool or a taxi.