A small market open only on Saturdays. A good variety of fruit and vegetables, meat , fish and sandwiches and cakes are the general things on sale. There is also a book stall.
One of Londons smaller markets.
Hampstead High Street has a nice and very very expensive shops, its nice walking and looking but not always possible to buy everything... well at least not for me right now..
Also in the heath St. you can find some real nice shops.
But trully, i'd say dont waste your times on that..better explore the amazing streets and allyes of Hampstead !