If you have the Rick Steves guide to Amsterdam, you will see the Hema department store briefly mentioned. The store in the central station was our mecca. I bought a cheap but good-looking black sweater there, and we twice loaded up on wine, croissants, cheeses, and delicious prepared foods such as sandwiches and wraps. Everything was HIGH-QUALITY and cheap. The prepared food was better than we got in some restaurants during our European trip.
EDIT: Thanks to Sam, who noticed that I said everything was "low-quality"--the opposite of what I meant. I shouldn't have written this report while I was jet-lagged. The wraps and sandwiches were better than any we've gotten in the U.S.