I bring extra cash for a emergency. I have purchased jewelry for cash, $350 for a ring is the most in a port, but I no longer do this as I found you can buy jewelry cheaper online at places like bidz.com
I would not go crazy with buying stuff in the ports. Nassau does have a nice staw market. I have bought junk jewelry there that fell apart later .. it wasnt that cheap, hand made.
I now stick to carved wooden things, or things that I know will not fall apart and that later on I will enjoy looking at. For instance I have a carved wooden frog bank I got there. I also paid $35 for a nice leather purse that now exactly fits my tablet.
Tips are $11.75 per person per day but will be charged to whatever credit card you put up.
Other than what I buy in the ports .. perhaps a taxi ride to town for instance, thats all I buy in cash.
I put at least $50 mostly in ones, a few fives and a ten in a envelope and take half into each of the two ports. You will want to barter and they dont always have change. Tips to shuttle drivers, at the airport, baggage handlers, that sort of thing. I find I always run into people I need to tip a few bucks each.
Conquest 7/21/13, Miracle ALASKA 8/27/13, Miracle HAWAII 9/17/13, Celebrity Summit, 11/30/13, Celebrity Summit, 12/7/13, Celebrity Constellation, 2/7/14, NCL Epic 3/2/14, Allure 5/4/14, Allure 11/2/14, Quantum 12/8/14