Ripper Update So, I went to Petco yesterday and got Rupert some things to redirect his chewing instinct.
→[More:] Some doggie rawhide strips, which he'll pick up and carry around or bat around for a little while, but they don't really turn him on. A puppy kong (they were out of the cat kongs), which he is interested in when I fill it with treats but not afterwards. I also got a bottle of pure lanolin, which at some point I will try spreading on those things to make them smell like wool and be more chew-desirable. He still loves the sock monkey toy, and I found it in my bed again this morning. I suppose I should quarantine it because it's made out of cloth and has fiber stuffing, but he does love it so much.
I also talked to the vet and they said I shouldn't worry about what he's swallowed unless he starts actively showing signs of being sick - which I know how to watch out for after having elderly cats with chronic illness for so many years.