I buy pesto sauce from Aldis. They come in little glass jars.

I use them to portion out protein powder. So instead of 1 big plastic jug, I have about 50 little glass jars.

Each one a single use that fits easily into my gym bag.

For bigger ones, like pickle jars, you could fill it with candy, or pasta, or coins, or cereal.

Stays fresher longer sealed in glass, than just in a plastic bag inside a box.