I have a lot of foam noodles in my hulls and mast. They're cheap and they provide a lot of floatation.

This year I added floatation bags. You can buy the really good bags typically used on monohulls but the cheaper bags made of PVC are a good solution for beachcats.

I use both the noodles and the bags. During an accident there is the possibility that the bags would be punctured inside a fibreglass or carbon hull but the PVC is really durable. The bags will not be inflated tightly so they should be able to bend with the hit. If they are punctured though, the noodles will still work. I've heard some say that the noodles will soak up water but I think that observation comes from seeing those that are left in a swimming pool for weeks. If something happens on the boat for the amount of time it takes for the noodles to become waterlogged you should carry a waterproof VHF to summon help a lot sooner.

I recently read of a Star restorer who bought five thousand ping-pong balls and placed them in netting.