I would think of starting with the basics: marshmallow, kitchen sponge, soda.. Then maybe something more fun like one of these squeeze stressballs. I'm sure actually doing it might inspire other things to put in there, plus hearing suggestions from others.
It's called many names but the one I got was Panic Pete from Amazon, it's $11!
Dang, she's like one of those Panic Pete squeeze toys.
Schylling PANIC PETE SQUEEZE TOY https://www.amazon.com/dp/B001R57O88/ref=cm_sw_r_u_apa_i_L-yCFb1A9K0Z9
I believe that’s actually a Panic Pete.
https://www.amazon.com/dp/B001R57O88/ref=cm_sw_r_cp_api_i_xNKWDbDHSFAG8
I'd say it's one of these stress toys.
https://www.amazon.com/Schylling-PANIC-PETE-SQUEEZE-TOY/dp/B001R57O88
Amazon has it listed as Panic Pete
Positive I've seen them in at least 3 films.
https://www.amazon.ca/Schylling-Panic-Pete-Squeeze-Toy/dp/B001R57O88
You were the model for Panic Pete weren't you?
Don't know if this might help but, I recently ordered this medical toy lol:
Schylling PANIC PETE SQUEEZE TOY https://www.amazon.com/dp/B001R57O88/ref=cm_sw_r_cp_api_i_6cqRCbV14P2Z8