There is a small Riteway right next to TMM base, very short walk. We have done all of our provisioning there before. But, we are fairly simple and eat most meals ashore. It had everything we needed. YMMV.

You might consider ordering the bulk items for delivery and shopping at the Riteway by TMM for your fresh goods if you are not too specific on what you need.

EDIT: If you're up for driving on the left, and on very steep hills, we also always like to rent a car. It gives us the freedom that we really like. Anyways, I'd also recommend looking in to that.