If you are going to go to the Bahamas, then you want to make sure that you know what you need so that you don't get stuck in some limbo somewhere between the US and the Bahamas. Making sure that you have everything you need shouldn't be all that hard, and it will make your trip much less worrisome.
To get into the Bahamas from the US, you do not necessarily need to have a passport. However, you will need to have at least an enhanced driver's license or state ID. Not all states offer this level of license, so you will need to check to see if your state does offer it. If not, then you will need to have your passport. You can either the booklet or you can get a passport card. If you don't have a passport, you will need to start planning early, since it can take several weeks for your passport to get to you. However, while you do not need a passport to get from the US to the Bahamas, you will need to have one to get back to the US. If you are flying home, you will definitely need to have your passport booklet.
In general, you aren't going to need to have a visa in order to visit the Bahamas. However, if you are going to spend an extended amount of time there, you may want to check with the Bahamian government to see if they are going to require you to have a visa for a longer stay. You can do that by visiting a governmental website or you can contact a Bahamian embassy. You should be able to apply for the visa at that point, although you may also be able to apply for one while you are in the Bahamas if your plans have changed and you have decided to extend your stay.
Some countries require you to have vaccinations before you enter them. Those vaccinations are for your safety and protection to help you fight off illnesses that you may not otherwise encounter. The Bahamas is not one of those countries, so you don't have to worry about making sure you are current on your shots. However, you may want to make sure that you carry info about your health in general, just in case something happens to you.
The Bahamas are an island paradise. Make sure that you are ready for everything you need before you get on your air charter to the Bahamas.