I bring just a couple hundred $US in cash and my left over JA$ from prior trip to get me from airport to Negril.
I bring 1 CC (the one with no foreign fees) and use it for big purchases - like hotel and car rental (World MC covers the CDW - HUUUGE savings).
I bring my ATM - but just as backup and try not to use it. I've used it in the past but got local ATM fees + my bank fees + 3% foreign exchange fee (~$17 total on $300 withdrawal - way too much for me). So non-Canadians w/out Scotia - be careful on ATMs. Try it once, then login to your bank next day or two and check your fees. I recently switched banks - so will try the ATM next reach and see if fees are more reasonable (this one at least has no 3% foreign exchange fee).
For my daily spending cash - I cash Travelers Checks for JA$.
I like doing it daily because forces me to stay on my budget - once that daily "allowance" is gone, my drinking is done.
(NOTE - have to be careful to plan for weekends and holidays when cambios/banks are closed).
But I also always keep the prior referred to backup stash of 1-days spending - just in case.
TCs used to be free at AAA but they started charging a few years ago (at least in Dayton, OH) - luckily they are still free at my bank.
I use Banmark when staying on the West End and the one in front of Bourbon Beach when staying on the beach - never a problem.
Actually, they only need me to bring my Passport on first visit each reach - after that, just my license - very convenient.
I've used them at cambios all over the island - Negril, Ochi, Treasure Beach, Port Antonio, Mandeville - and no problem.
BUT last trip (March 2013) we spent the last 3 days in MoBay before flight back.
Not one cambio there would take them - even with passport and 2 IDs. They all said I have to go to a bank for TCs.
If you've never been in a JA bank - that meant a several-hour wait in line. So never again trying to use TC in MoBay.
If that practice spreads to Negril, I'll have to figure out another method.
One final point, whatever method you do...I strongly advise NOT having the cash for the whole trip in one place.
Check posts here and other trip sites like TripAdvisor, and you'll find posts of even people leaving valuables in hotel room safes being thiefed.
That's why I like the daily w/drawal - my money is on me, not in the room (except a little stash) - and that way no more than $200US is ever at risk of loss, theft, drunken mistakes, etc.
A loss of that amount would suck - but my vacation would not be ruined.
