Depending on which dock you are at in Cozumel there are shops, bars within walking distance
has lots of info
Belize there are shops in the port area and if you stay in the compound but go past the shops there are a few locals selling their stuff.
Alexandr Pushkin, Carnival-Holiday, HAL-(old)Westerdam, Orient lines-Marco Polo, Royal Olympic-Olympic, NCL-Dream, Dawn-Princess, ACCL-Grande Caribe, Oceania-Insignia (3), Regatta(4) Marina (1) St Lawrence Cruise Lines-Canadian Empress
Scenic River cruise June 11,2012