You said "Simpson Bay". Where exactly in Simpson Bay? Do you mean Simpson Bay Resort?? If so, Market Garden is in walking distance, at the corner of Billy Folly Road. Market Garden is relatively expensive. They have a reasonable selection, but not nearly as large as some other stores. If you have a car, Carrefour on the Dutch side or Super U on the French side have the best prices. There is also Maho Market in Maho. Maho Market has decent first day supplies. There are several other smaller grocery stores.

It also depends on whether you just need a few things, or you plan on cooking in a lot. Also, if you're looking for wines, costs vary widely across stores. If you like French wines, in particular, look on the French side. US wines are WAY overpriced on island. Prices for things like liquor and wine at Market Garden are pretty high. It really depends on what you're looking for. If you want US brands, you pretty much need to focus on Dutch side stores. Understand though, those products will cost much more than in the US. Carrefour and Super U have their generic forms of many products, so those will definitely be cheaper than US brands.

Please post any other specific questions you have.