This may be old news, but I just ran across this video and thought it was a GREAT idea! Cardboard TP tubes as a disposable STP.
https://www.youtube.com/watch?v=Ykecx17wY8M
New to me but I mostly feel the urge to stp when I'm with new friends or strangers. I feel like I've tried almost everything. My favorite on-the-fly disposable stp is a drink lid from a fast food restaurant, but that only works in neighborhoods that have fast food restaurants. There are none in my current neighborhood, so I've recently started carrying a go-girl in with my bike tools.
I will give the toilet paper tube a try soon.
On a side note, I'm kind of irritated that google owns youtube now. I don't like being constantly offered videos similar to what I watched last, even when what I watched last was really cool.