Hi!

Have you been to St Martin/Maarten before to know your way around?

As you are spending a night on the Dutch side at Mary's Boon, I'm guessing you will take a taxi to the boat? You could hit the Carrefour across the causeway and get the things you want.

Or, as has been suggested use:
https://www.shopndropgrocerysxm.com/

Happy hours...Grand Case has Calmos Cafe or Rainbow

If you go into the lagoon, Simpson Bay Yacht Club, Dinghy Dock, Lagoonies.