I use freeze dried raw meat. Given the paper will be tossed (keep track of it) you could use frozen/thawed chick's, mice, etc
Ferrets: Contessa, Frankenfurter, Butterscotch. Kitties: Watson, Oskar DIP Sinnead, Vincent, Boris, Zeus and Athena, Willow, Mr. Frodo, Indie, Lucrezia, Judge, Odin, Miss Emily, Suki, Cody, Aristotle. RIP Herne, Ligeia, and Mr. Stubbs
I notice that a lot of people are mentioning toilet paper rolls, and I would like to provide a warning.
My little guy was playing around in a box full of rolls that I had saved up for him. Next thing I know, he had pushed his head into the roll by running into a wall and could not pull it back out; the fat and flesh on his neck just bunched up. I had to tear the thing from around his head to get it off. Then, I spent a good ten minutes having to remind him to breathe while he lay in my lap. It was terrifying, and we don't let him around them anymore.