I don't. I put them in a 48 Oz. Nalgene including my spare tube and Topeak Mini Morph (got lucky that it fits). Nalgene is 7 Oz. and very waterproof and floats...I have it on top of my rear rack when using no panniers and in the panniers when they are on.

It does take some skill to get items in/out of the Nalgene.