Do you know of any quiet or discrete fidget/stim toys? I find that I need to fidget in my school discussion group to keep from getting super anxious, but if I play with a hairband under the table or…
I’m going to second the doodling thing. It’s not the most effective fidget I use, but it is pretty much accepted as par for the course since a lot of people do it.
If you are allowed to keep personalized things with you in the classroom it sometimes helps to pick a theme. For instance one of my coworkers is a hello kitty fan. So nobody is going to think twice if they see her playing with a Hello Kitty koosh ball or fuzzy pen topper.
It doesn’t read as unusual to people because the read it as hobby related like knitting or drawing.
The other thing is ‘cool factor’. IE if what you are playing with looks cool people think 'I want to play’. Kinetic sand and perpetual motion/magnetic toys are good for making everybody want to play with them. So nobody will think it is odd for you to play with them.