Personally I love Palace Casino, nice friendly staff, fun, and you will meet alot of locals for chatting. I only play the slots, and win enough to keep me playing.
Shops mentioned above are all great.
Ramon's gift shop has a wide variety of really nice things.
If you get over to Caye Caulker, go to SilkPainter's Art shop, great selections.
On Pescador in San Pedro, The Beauty of Nature Gift Shop, great colorful art, including wooden chairs and tables, that are easily carried home.