Shelly (is that your real name? - you obviously belong on the beach!)
We did the cave tubing trip in 2002 with Seaduced. I would recommend them. The trip included a visit to the Belize Zoo, lunch at Jaguar Paw, and then the cave tubing. Oh, and lots of rum punch. There are a couple of boarders here who may be able to vouch for that! (Mountain Larry, v-ballcoach, Gela, etc.).
We haven't done kayaking, but would love to, so let us know how that goes.