Whether it's in my boat or kayak, I practically never go on the water without my GPS. Not only can I use it to determine where I am, I can also use it to find my way back home and download my tracks to show where I went. I spend a good amount of time on the water exploring new paddle trails, and the ability to download my latest travels comes in really handy.
One of the neatest things about a handheld GPS -- in my opinion -- it that it allows you to overlay your track on Google Earth, same it, and send it to people as an illustration of where you paddled, caught the big fish, saw the dolphins, or found a secluded beach. Or else, say, "Here is where we went on vacation. Eat your heart out."
On my boat, I keep my handheld GPS plugged into my VHF radio. It continually displays my Lat/Long and if I happen to get into trouble, pressing the distress button will alert the Coast Guard of my exact location. Again, I typically download my travels when I get back home.
This project is the height of simplicity, and it's cheap, too. For it, you need a small piece of marine polyethylene, some stainless steel screws, and a pair of rubber pole light mounts (such as used to hold your running lights when you are cruising in the daytime.) Along with a few rubber bands, that's it.
In use, the mount snaps around the metal handrail on your boat's console.
Step 1: This Is a Pole Light Mount
Step 2: The Mount in Action
Using a couple of screws that won't penetrate the plastic, attach the two rubber mounts.
That's pretty much it.
Now all you have to do is use a couple of substantial rubber bands to hold your GPS to the mount, and attach the mount to the hand rail. I have used mine in pretty rough conditions and it stayed put.
I have a chartplotter on my boat, but I use that to navigate by. I like to have the second GPS to record my tracks, to show my speed and course, and to look up waypoints, etc. I find it is easier to use than my more expensive unit.