Thank you for the thoughtful response. I failed to think of a wide-brimmed hat and portable water filter. Also, I have a Camelbak but probably would have left it at home had nobody reminded me.
I call it "Tourist Pragmatic". Not a lot of survival gear but some stuff that you might blank on. It sounds like you'll be in proximity to a decent hotel so shelter and camping gear seems a bit much.
Couple other things I might add:
-packable ponchos - I don't know when the rainy season is in Belize but they might pay off.
-an Aloksak/otterbox/drybag for your kayak trip.