It is fairly easy to charter a trip to Tobacco Caye from Dangriga, and if you do make reservations for accommodations the resort may make these arrangements for you, be sure to ask. The cost of the boat transfer is not included in the cost of your accommodations, and is usually $35 BZ each way if you get on one of the regular trips out to the island.
If you are arranging the trip yourself, there are a number of ‘captains’ who make daily runs to the island. If you ask around at the Riverside Cafe in Dangriga, someone will be able to take care of you. I realize that sounds a bit sketchy, but it works out, just keep in mind this is Belize and things are a lot more laid back and less structured than most of us are accustomed to. The Riverside Cafe is located just east of St. Vincent Street, across from the docks on the south side of North Stann Creek. Most of the boats leave in the morning at 9 am or noon, but later trips can be arranged as well.
The trip itself takes in between 25 - 45 minutes depending on the surf, the bigger the surf the slower the boats go. The boats that make the trip are not custom cabin cruisers, and instead are open boats approximately 20 foot in length, so do not expect to stay completely dry on this trip, more often than not you will get at least a bit of spray from the boat. The captains are however very good about covering your gear and suitcases with a tarp so they stay dry. My daughter made this trip when she was one and a half, so if she can make it, so can you.
If you have a rental vehicle, there is no designated secure location where you can leave your vehicle; you will need to make arrangements to leave it in a place where it will be safe. Again, you can just arrange this with the boatmen at the Riverside Cafe or one of the resorts in Dangriga for a small fee. I was a bit nervous doing this, but our rental truck was exactly where we left it when we returned from a few days at the island. The bottom line is that tourism is the life blood of most of these folks so you actually have little to worry about.