I would suggest packing it in a dry bag. If you pack it right, you can have enough air in it so that it will float. A couple of items you might want to consider adding:

One or 2 lightweight tarps (for shelter building).

Parachute or similar nylon cord (a million and one uses).

One or more ensolite or similar pads (insulation, splint building etc).

At least 1 SOL bivy bag (ideally one for each person). I don't think the "reflecting body heat back to you" helps that much, but keeping the wind and wet off of you is huge. I now always have one in my daypack. See http://www.adventuremedicalkits.com/product.php?product=144&catname=Shelter&prodname=SOL