Elbert's comment is really useful - you do need cash, and small denominations are better than large.
Rubber boots and/or hard-soled shoes - a must.
Also recommend extra ropes, axe and crowbar.

Communications are another interesting aspect of an event like this ............ if your house is like our house, the phone rang a bunch last night right after CNN or TWC got excited about Dean. Soon the phone lines for Belize will be jammed up and that will freak out your family more than even a Fox News live-hystericast.
Suggest that you select one contact person who is out of country, and out of the path of energency. Have that one person be your one outside contact - in the event of a problem, you call them (not the other way round) and people can call this contact person instead of trying to get through to Belize. Once that contact tree is established, inform friends and family.

other things you may not have done yet ........... back up computers now - put important items on a couple of discs or sticks or whatever, put in ziplock bags and stash in safe (dry)places.

AC is not likely to get hit by Dean -- but there are inconveniences that can happen anyway --------- shipping can be disrupted and that can result in shortages of things you really need ......... in particular medications, contact lenses, gas and diesel. Put some extra away today.

We like to have fresh water easily available if power crashes, which it will do in a storm. Suggest two or three clean plastic trash cans --- one in kitchen, another in bathroom(s) --- take hose and fill them with freash water.

From what I can tell, NEMO has it's act together - and they say we're reasonably clear of danger - thanks Jim !