Tender from ship to shore an interesting experience. Not much to see in Belize city but you can walk around the streets, maybe visit the museum before returning to the inevitable tourist trap shopping where you can buy things you do not need or have a reasonably priced drink before returning to the ship
Nice harbour and looks like a Caribbean island, which it is. The town is a short stroll away. Nothing exciting but nevertheless interesting to see. You can take a boat and laze on a beach for a couple of hours or find a little bar at the water's edge and relax and absorb some local colour. In case you did not find that special gift there are shops at the quayside.