Socks also work to tie the leg ends closed. And shoelaces. Especially with thick, stiff, or slippery leg material, with socks you can get a stable knot while sacrificing less air volume. With rubberized gear, you can fold over the end first.

As others have pointed out, beware planning for one environment, and finding yourself in an very different but adjacent one. Warm air, cold water, no pants.

I learned how to do this in Boy Scouts years ago. I doubt I could do it now. Especially in a survival situation.