Start with an empty toilet paper roll, or cut down a paper towel, wrapping paper, aluminum foil, etc. roll.
(click to enlarge to properly take in my nail polish)
Think of one end as having four points (as in a compass or and X), and fold down the edge at each point, overlapping the edges so the bottom is closed off.
Use your fingers, or if you have stubby little short finger like me, a stick of some kind, to flatten out the bottom.
At this point, it is a perfect little container for cotton swabs, pens, brushes, scraps of thread, cotton balls, and just about any other small objects.
If you're using it as a treat tube, add the treats. My cats don't really get treats, but they do get a second brand of dry kibble, that they think are treats. I'm cruel.
If you have a small animal (rabbit, chinchilla, hamster, etc.) you can add fruits (try mashed banana), seeds, peanut butter, or special treats you don't want them to devour all at once. It also provides them with a bit of enrichment. Please check with your vet before offering these to your pet, and before giving them treats of any kind. Each species is different (chins are especially sensitive). They will use the tube differently than a cat, and will probably get at the contents by chewing up the tube. Cats will just knock it around until the treats fall out.
Once your cat has figured out how to get the treats, you can make it a bit more challenging by folding down the sides on the other end.
Present it to your cat while he sits on his personal pillows. Actually, it's probably best not to offer it to your cat on your bed, unless you enjoy sleeping on sharp treat crumbs.
If you have multiple cats, you'll want to make multiple tubes.
Pretend your cat isn't completely disillusioned, and actually enjoys the lovely gift you've just presented him with.
You might want to give the treat tube to your cat in a somewhat confined space until you know how much it is going to get knocked around. It's not fun to step on wayward treats (or kibble).