Yes and yes. On St. Maarten and St. Thomas/St. John, most of the public beaches have restrooms and at least a snack bar of some kind. On St. Maarten, Great Bay beach is right near downtown Philipsburg and has plenty of food options nearby. The other two I like on this island are Dawn Beach and Little Bay beach. Both have restaurants/restrooms.
On St. Thomas, Coki Beach, Magans Bay, Morningstar Beach (on St. Thomas), or Trunk Bay on St. John are all similarly equipped.
Enjoy.