Individual responsibility is key for ensuring safety on the water. Everybody who goes boating should know their responsibility, the rules of the road, the dangers posed and how to deal with them.
 Skipper Responsibilities
If you are the skipper of a boat, you are 100% responsible for your vessel, your own safety, the safety of those on your vessel, and any damage or harm done by your vessel colliding with swimmers/vessels/property. If you are the individual who has rented a house boat you are the de facto skipper, unless you have a firm & clear agreement with someone else to take on the responsibility. When you raft up with other vessels you assume shared responsibility for ensuring that all of those vessels are properly secured. if the raft drifts all the skippers share responsibility for any damage done to other vessels or property in the case of collision. if your vessel is damaged as part of either the normal operation of the raft or in the case that the raft drifts, you are responsible. If anyone is injured on your vessel whether a guest or part of your crew, you are responsible.
At all times including when at anchor, there should be at least one individual capable of safely operating each vessel (i.e. not inebriated). When the skipper entrusts operation of the vessel to another individual the skipper remains responsible (i.e. the skipper can get drunk and have a DD but if the DD screws up it's the skipper's fault for not picking a better DD).
DISCLAIMER: I Am Not A Lawyer. This is my layman's understanding of common law and good manners. This should not be interpreted as legal advice or and indemnification against liability.
 Guest Responsibilities
When you are a guest on someone else's boat it is normally important to receive permission before coming aboard. In the case of a raft-up this permission is essentially implicitly given for boarding for between 2 vessels that are adjacent. If you wish to board from the water or from a small vessel you should ask for permission explicitly, unless it is at a communal dock or ladder. This ensures that you board the vessel in a safe manner, and that you are welcome on the raft in general. The implicit permission to board a vessel in a raft is meant to allow freedom of movement and does not extend to entering the cabin or taking/borrowing/making use of any of the property or equipment on the boat.
 Boat Safety
This is not a comprehensive list, but boats >16ft with a motor must have:
- One PFD per person on board (does not need worn, except in the case of small children or inflatable PFDs)
- One throwable PFD (horseshoe or ring)
- Day & Night distress signals (flares, strobes, etc)
- Audible signal (bell, whistle, horn)
- Fire Extinguishers (quantity depends on vessel size)
- Proper Documentation
For more info see The ABCs of California Boating
Platforms probably count as recreational floats that wouldn't be subject to these regulations. However, platforms that people are sleeping on should be equipped with the first three listed above.