Places to visit... Take the ferry to Isla Mujeres. Get a local to point you towards Playa Norte there. You will be back in Cancun to have dinner. Thank me later ;)
Xcaret is a very nice trip - will take the entire day. Make sure you stay for the evening show. Soooo worth it!

Places to eat... hmm we went all local on recommendations and can't remember any of the names. There's a steak place in Playa del Carmen (El Diez or something like that) which is pretty good. Nothing wow, but makes a mean steak - you chose the size.

I have listed some of my picks for great day trips and beaches on my website/blog. Link is in my steemit profile.

Enjoy the trip!