Here's one that I can share, that has been very useful. I took a foam camping (sleeping) mat that I got for $5 on sale and traced on it from a cardboard pattern that I formed around the inside back storage pocket on my float tube. Cut it out and hot-glue-gunned it together. Then I cut an "H" shape slit in the top for an opening. When I go out for an all day float, I put my food and beverages in the cooler and top with ice. In 90 degree weather, the 'soda' stays cold for at least 4-5 hours.