|Left: yarn bits. Right: stitch markers|
I like to save them in a coffee mug near the couch where I usually knit. If I start a project that requires stitch markers (anything knit in the round like mittens and hats for example) I pull out a small bit of yarn. I make a loop and knot it twice. Voila! Homemade, basically cost-free, from-trash-to-use...stitch marker.
I use these for knitting only, not crochet. I've never used stitch markers in crochet, but I am pretty sure they are claspables, like safety pins. If you used one of my stitch markers, you'd have to cut it out because it would be stuck in your crochet (which, I suppose you could do if you don't mind!).
You can definitely purchase stitch markers at any yarn store, they are usually made from plastic. But why buy something you can make for virtually no cost? Plus, if you lose one (and they are pretty small) it's no big deal because it was scrap yarn. Yay!