You are supposed to pack out the poo on Whitney and Shasta. The Forest Service gives you poo bags with cat litter along with your permit. So far they do not check your bag upon leaving! I can just see it -- busted and fined if you do not bring out a certain amount of poo!

You can buy plastic bags that are odor proof. They are intended for things like fish guts in bear country- but should work for TP and poo also. You should be able to find them in a fishing store.