The pictures are where they are going to get you.. I bet its going to be $25 for a pciture maybe more. Most things can be purchased with credit card (use a capital one card or you will be paying a foreign transaction fee on every purchase) but you should bring cash to pay for the little things.
Taxi- around $10 to $12 each way., snorkel rentals may be included in the park admission (go online and google on Chankanabb and you can typically find a coupon to save money.) You might also be able to pre-pay for your tickets so you don't need cash for them. But you would be amazed at how fast you can nickel and dime away $40...
I'd bring $100 in cash in small bills. Get a waterproof case so you can keep your cash,credit card and cruise cards with you in the water. Make sure it has a cord that you can tie to your swimsuit so you don't lose it in the water.
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise
NCL Dream October 2006, RCCL Mariner OTS June 2007