Add polymer clay. Polymer clay isn’t for everyone, but if you’re comfortable with it, it’s a very distinctive, very cute way to upcycle a glass jar; Living from Scratch offers this easy tutorial for covering a jar lid with polymer clay. This would be a great project for a storage jar that will be in easy view, and thus can handle being highly decorative.
Add a pour spout. The Tip Garden used the top from a cardboard salt container to turn a Mason jar lid into a jar with a pour spout. If you make your own taco seasoning or ranch dressing mix, etc., this is the project for you!
Paint with chalkboard paint. My Handcrafted Home used just a few coats of chalkboard paint to turn a glass jar lid into a writeable, wipeable jar label. This project would work well for gift jars (perhaps containing homemade granola?) or for turning little baby food jars into spice jars that might have ever-evolving contents.
Stitch on them. If you’ll be using your jars for non-food storage, check out how you can embroider on your jar lids! This project would work well for jars that will be used to store sewing supplies, especially bobbins or embroidery floss.
Decoupage them. Covering jar lids with paper completely changes the look of the jar. If you cover baby food jars, you can even use a large-format hole punch to cut your paper, saving loads of time and fuss. Or you can work with smaller scraps, decoupaging found and recycled papers. This project would work well for any non-food storage, such as craft supplies, hair pretties, or collections.
Glue stuff to them. There’s a trend of gluing toys to a jar lid, then painting the whole thing a single color. If you can bribe the requisite toy animals away from your kids, then it’s a great project to give back to them for storage of all the little collections that kids have–bottle caps, interesting keys, random rocks, etc.
Crochet over them. Crochet jar lid covers are very pretty, and save you having to do any refurbishing work to the jar lids themselves. These work well for jars that you don’t access often, but are still visible–jars on open kitchen or bathroom shelves, perhaps, or those containing keepsakes.