I love valve-compression dry bags for gear.
I've got a 5-liter bag that I store my first-aid and survival kits in. The bag rides in the day pack when hiking or hunting but clips in the canoe when we're on the water. There's no need to have separate first-aid and survival gear kits.
The cool thing about these bags is that after you load them, you open the valve, rolled down and clip the opening. The air flows out and compresses down for easy storage. Then close the valve.
My bag is by Pacific Outdoor (http://pacoutdoor.com) and I got it at Sierra Trading Post. They range in price starting at $25 to $30.
I recently got a larger one that my daypack fits in. That way the daypack goes in the bag and into the canoe when we are floating. There's no need to transfer gear out of the daypack and into a dry bag every time we switch from land to water.
Valve-compression dry bags come in handy for a lot of uses on river trips, hiking or for backpacking. They are very lightweight compared to other dry bags.