Breathable trail runners for river crossings.
The walmart foamy option is fairly durable (about 20 nights of heavy use, but a pad will make about a dozen pairs), very stable, ridiculously cheap and ultra comfortable. About 1oz for the pair.
Step 1: Buy $4 Walmart blue foamy sleeping pad
Step 2: Trace your foot and add little less than a cm all around (you can trim to fit later, though I find a little extra is kind of nice and you don't trip over it), and add wings so that when folded up together it looks like an Adidas shower sandal
Step 3: Cut foam
Step 4: Apply 1 piece of duct tape across the top - you may have to shorten the wings after trying on to get a tight fit.