I carry my cameras in a 5 Gallon sized dry bag that I place a towel in the bottom in case any water might get in it, which hasn't happened since I started using it in the mid 1990'.

I had an extra optical port for my underwater housing so I cut a circular hole in the dry bag and cemented it onto the bag with a melting glue that is used for fiberglass. This allows me to take photos with it of fish underwater as I dunk the bag below the surface. I have to shoot blind, but if works for me.

In really rough water like river rafting I will attach the bag to a part of the craft using a caribiner. (sp)

I normally have one camera sitting in the top of my day pack where I can reach it quickly so it is completely stored. Don't ever set a camera on a boat seat, that is an invitation to drowning unless it is a waterproof model.

Here's a few images done with the dip and dunk bag.

I would think a waterproof P&S would be the best for most folks.