I made my own stepper using two different diameters of PVC pipe, adjustable nylon straps, 1/4" nylon braided rope, & stainless steel caribeaners. Here's a link to a quick video I made. I can provide more details if needed.
https://www.youtube.com/watch?v=glCDq7BerKAMy girlfriend and I made a water bag that I got to try out this past Sunday. We picked up a piece of rip-stop nylon from the local fabric store, sewed it into the shape of a simple bag, and also sewed 1" nylon straps down the sides and around the bottom to give it the needed strength. We also sewed a 1/2" diameter length of rope around the opening to make filling it easier. Overall, it worked great. One modification I'm going to make before the next solo outing will be to add a second strap at least 4' long that will attach to the bag and then 4' back on the existing strap. The problem I encountered was getting the strap to stay on my shoulder. It kept wanting to slide down my arm. Adding a second strap will allow me to put a strap on either side of my neck & keep the bag centered. I want at least 4' on the second strap so that my head will easily slide out as the boat rights itself.
I now have the confidence to take it out under any conditions and not worry about getting stranded!