If you are able to fish, chances are you're not going to have the temperature dropping that cold at night that you won't do just fine in a 20 degree bag with some clothing on.

Oh, and if you are taking stocking foot waders, trailrunners or boots can do dual duty as wading shoes as long as you don't mind waiting for them to dry afterwards. However i've found most of the time unless it's a dedicated extended fishing trip that I am packing in a belly boat for, I don't mess with waders for small streams and the like. I just ensure I have warm long johns with dry socks and camp shoes and I wade and get wet during the day in small streams - and take fairly minimal fly gear. Wading in long nylon hiking pants is usually ok for small bits and they dry quick.