I slice up plastic containers/tubs, such as one-litre yogurt tubs, with ordinary scissors or kitchen shears, into strips about half an inch across and 6 inches long, and I write on them with a grease pencil. Just the plant (eg lettuce, green beans) - the specific type etc are recorded in the garden book, not on the label. I write in the top half of the strip and then just stick it in the ground.
I've had the same grease pencil for over 20 years. I may need to replace it in the next decade or so. I keep the tags in the fall and reuse them if I am planting the same stuff later (and most of us usually do plant the same core things all the time.) Where I live, we can recycle those tubs, so any strips I don't want any more can go in the blue box. As an extra bonus, some of them are written in the "brand new to writing" handwriting of then-small children (now grown), giving me a little nostalgia as I look through them to find the one I want, a bit like putting kindergarten-made ornaments on my xmas tree.