Belize we did the zip line excursion through RCL. Had a great time. It is a long 1.5 hours drive both ways, however. Our guide was very funny and told us a lot about the history of the country. On the way back everyone slept! Lunch was provided. OK food and there is a bar for purchasing drinks. Nothing really is around the port except the normal port stores. This seems to be a port you'd want to visit just a couple of times.
Cozumel - Jumped in a taxi and went downtown. Walked through shops and some interesting bars for most of the day. There are some good restaurants if you go a block or so off of the main drag. Had planned on going to the beach in the afternoon but had too much fun in town. Quite a bit around the port also if you need to kill that last hour before boarding. There is so much to do in Cozumel you could stop there every cruise.