This is a small collection of things that I printed to make a kayak safety flag and light. It uses a fiberglass driveway marker found at most major hardware stores (1/4" long and comes in 4' and 6' versions. The Scotty mount was designed by Prestonf and can be found at http://www.thingiverse.com/thing:793219. I have included one of his models in this design. It fits a Scotty mount perfectly.
The LED is a vehicle replacement wedge type bulb. These can be found on superbrightleds.com or on Amazon. Just search for 921 wedge LED. There are lots of them to choose from. They are extremely bright and run on 12V (I'm using an 8x AA holder which will run for several days constantly). I recommend using the cool white as it does not seem to attach bugs or mosquitoes.
The "lens" for the light is a piece of 1/2" ID 5/16" OD vinyl tubing. Just cut it to your desired length and assemble. You will need to drill a small hole for the wiring to pass through the base.