I think cat-holes have been covered but I just wanted to throw another variable into the equation… pit toilets. Hiking in areas like the enchantments, N. Cascades, or on trails around Rainier, pit toilets are plentiful and should be used to the best extent possible to prevent the rest of the park from turning into a cesspool. (yeah yeah yeah… “I avoid those areas, too many people, NPs are the devil, blah blah blah”).
In these areas, I like to use biodegradable baby wipes for a couple reasons: 1) don't want to (and shouldn't) throw used rocks into the toilet or disperse them into the woods. Also don't want to pick leaves or other fauna for TP in a high traffic area 2) takes fewer baby wipes to polish off the undercarriage than it does to do the same job with TP. I find one sheet ripped in half to be sufficient for the job.
Yokes grocery store will carry biodegradable wipes from time to time and you can find them online also. I'll lay them out at home to dry them out and then pour a little water on them right before I use them.
Packing them out is never a bad idea but even towards the end of season, I didn't find any volcano pit toilets on the Wonderland and think throwing them (biodegradable ones) into the composting pit toilet is perfectly fine despite the fact I risk a visit from the BPL inquisition for saying so.