Regular, disposable lighters can be carried on now. Refillable and "torch" lighters are still banned.
I would definitely take a water filter. I would get the bottle/straw type if not checking a bag and the full "horse" if checking a bag.
I'd also carry several energy bar type foodstuffs on the plane. And get a couple bottled waters once on the plane and as soon as you get off.
You might also what to do some quick research about where you will be staying and get a "lay of the land". Find out what is near your hotel, both in terms of potential threats and possible assets. I'd also do some preliminary research on alternative ways off the island and how to get to them from your hotel.
I always program certain phone numbers in my cell phone. If I'm flying, I alwasy have a couple numbers for the airline I'm flying on, a substitute, and a travel agent (hard to find these days). If my flight get's cancelled or delayed so I miss a connector, I can be the first on the phone, even while I'm standing in line at the ticket counter.
Lastly, I have a belt with a zippered compartment on the inside where I can stash a few bills. Don't touch them unless there's an emergency. Don't do $100s, do smaller bills. Noone is going to make change for you in the DR in an emergency situation. And $5 $10 will go a long way.
Finally, make sure your credit card issuer knows you are going. Some banks, particularly credit union, cut off your card if they see it being used in certain countries without prior notice. I learned this the hard way....twice.
Finally, finally, I always treat the staff where I'm staying with sincere respect, and I tip decently. Don't tip too much or you advertise that you have lots of cash on you, but tip them early. You'll get treated better and it might just help in a pinch.
Also, check the U.S. Dept. of State for background info and tourist warnings.
http://travel.state.gov/travel/cis_pa_tw/cis/cis_1103.html
Don't know when you are going, but the three most likely scenarios I would be concerned about currently would be:
1) Hurricane. check noaa.gov before you leave to get a sense of what weather is headed that way.
2) SHTF in U.S. and getting back home. do the research on alternative travel opportunities, know where the U.S. Consular Agency office is on the island and how to get there.
3) Civil unrest in the DR, either generally or directed specifically at you (e.g. kidnapping) - know your surroundings, travel in groups, know the danger areas, be nice. Keep a low profile, some people love to hate Americans.
Flying in, I think a great deal of your preps is information.