Hepatitis vaccination?

Hit your local used clothing store. They usually have lots of out of season stuff.

I second the recommendation for bug spray. A couple of weeks after my honeymoon to Belize ten years ago, my wife pulled a botfly larvae out of my arm and I pulled a botfly larvae out of her scalp. I'm pretty sure that we acquired the larvae when we stayed in an open air cabana. Lesson learned - do not stay in cabanas even if they are more romantic. Please note that, while disgusting, bot fly larvae are pretty clean and typically do not cause infection. Do not cut the larvae out, you will cause more damage than will occur if you find another way to get them out. The larvae need oxygen, so if you put petroleum jelly over the wound, the larvae will start backing out to get the oxygen.

Think about bringing mosquito netting. Bring a watch or travel alarm clock, none of the hotel rooms (other than the Radisson Fort George in Belize City) where we stayed had clocks. Bring a battery powered lantern. When we visited Tikal (in Guatamala), they turned the generators off shortly after nightfall.

Bring some kind of spices. Damn, the food in Belize was the most boring food ever. Which was amazing given that the food in next door Guatamala was some of the best food ever. Bring soap - again this was not typically provided in hotels.

Try Marie Sharps (local version of Tabasco).

Get some permethrin to pre-treat your clothes from insects. Well worth it. As for nylon clothing, it is extremely uncomfortable in a hot/humid environment. A good choice would be a light, loose fitting cotton shirt and loose fitting cotton/poly trousers. Shorts should not be worn if hiking in the forest/jungle, too many things that stick you, sting you or potentially bite you.

Water bottles are more durable and cheaper than a Camelbak and also easier to use with a water filter. Filter all water.

Look up a doctor or clinic that specializes in travel medicines, they can get you the right immunizations, make the right entries on an international shot record and make other recommendations of a preventative nature for the specific region you are travelling to.

Considered Costa Rica? Could be a bit safer!

On a trip some years ago to Puerto Rico (A U.S. Territory) some of our companions were from US Customs and they were at a beach outside of San Juan and a group of nasties got between them and their gear. They lost weapons, ID and their wallets with pretty much everything else.
Awareness, awareness, awareness. Avoidance as well. Good luck!

Those are good tips, widget. I didn't know that about the nylon clothing. I'll pass then. Plus, I sweat a lot. Cotton/poly should be better.

How about this. Take the usual precautions, carry your usual EDC (with travel restricted exceptions), and ENJOY YOURSELF. Don't get so consumed with preparation that you neglect the adventure. After all, thats what traveling is all about. Have a great trip.

Coming from somebody that lives in the southeast (SC), nylon clothing is not automatically uncomfortable in humid weather. Just because you personally find it uncomfortable doesn't mean that it is to everyone. You should try nylon clothing yourself before just taking somebody's word for it on the internet.
Personally, I like nylon clothing because of how well it wicks away sweat, and tends to help you feel cooler. Cotton is nice, but it gets noticeably heavier when you've soaked your clothes with sweat, and it will not dry in that humid of an environment. If you wear all cotton, you will either be wet all the time, or changing your clothes throughout the day. At the very least, try some of the cotton/poly blends. Either way, try it for yourself, synthetics just bother some people.

second the comments of Speedemon...at 540heat calories/gram of water evaporated, 2 grams evaporated removes >1kcal or 1 food calorie of heat...I find it much easier to control my body temp with nylon or the high tech polypropylenes