Well, there is always the reliable cucumber or carrot on a condom. But other than that.... my only homemade toy was a "fleshlight" of sorts that I made with a diaper, tape and a mason jar. Needed quite a lot of lube tbh but I was surprised by how amazing it actually felt. Of course, my diaper fetish helped a bit to make the experience even better. Even now that I am older and have bought legit fleshlights, I think that homemade one is still one of my favorite experiences.