I too have a Costco card. They're very useful for non-perishables, and the cost differential (and relative quality) makes it worthwhile, even though I have to travel some distance and so only go by perhaps three times during the year. Using the credit card for routine expenses that you will pay off promptly is also a very wise idea. It builds the credit rating with no risk, and no undue expenditure, which means when it comes time to get a serious loan you will get a much better deal.

Suburbia -- the inexorable vortex! :D