How we usually did it, and take this for what it is worth and the type of group you will be going with, is that we all put a certain amount of money in, to cover the rental costs, gas, the basics, and food. That way no one person is being stuck for the costs of things you do not anticipate. Each person can bring their own snack and keep it for themselves by marking it. We also always did BYOB. Plan to spend your first day loading, looking for the perfect beach to park at, and getting a quick dip to cool you off. You will need it! We also have the first meal of the night prepared in advanced. There will be no time for that with setting up.
Here are some good cheats if you are not a seasoned house boater but want to give it a try:
Have the dock captain take your to a spot and set you up. The can also pick you up and take you home. You might say "Well what is the point of house boating them?" I understand what you are saying, but how fun will it be trying to figure out how to drive, park, set up, navigate, and ultimately have a problem on your dream trip. It cost for this service, but if you are like me, I am all about the camping in a great spot, not worrying about an accident or harming a very expensive rental boat.
Book in advance for the best prices. You can also look for people who own timeshares on them and rent them out.
You can order groceries to be put on the boat for you. Again, a cheat, but a worthy cheat if you are coming a long distance and do not want to find a store. Besides, that way you know what grocery bill to split before you go.