You can get the gear most anywhere but I would really recommend a $15 snorkel and mask from walmart or some such.
1) you can get something that actually fits your face
2) it will be cheaper than renting for even one day
3) snorkel and mask don't take that much room in your bag (flippers ARE worth renting for this reason, IMO)
4) . . . just think of how many slimy, mouths that rental snorkel has been in . . . yeeeechhh.
5) or have Famous Vincent take you out to the reef . . he'll take care of everything, equipment, the boat ride, and he will provide a nice tour of the reefs, showing you rays, eels, octopus, and all kinda special stuff you'd never find on your own first time out.