Plastic jars can be used for almost everything (cannot burn candles in them) that glass jars can. You can save the top and add a bobble to the top as a knob for storage.
plastic relish bottles, ketchup bottles, etc. are great for pre-mixing pancake batter for camping. Just mix it up, put it in the cooler, and then all you have to do is pour it into your hot pan ready to cook! Mayo jars are good in garages for nails, screws, etc. also, for kids catching fireflies, you can turn them into "lanterns" for the kids by filling with water, cracking a glowstick and tightly sealing the lid. I also use mayo jars to make salads in for home or camp. Put the dressing on the bottom, then a hard veggie like carrots or cucumbers, then layer other veggies and salad (even chicken) on top and close. They last anywhere from 5-7 days like that, and i find im much more enticed to eat them when they are already all fixed up and ready to eat, and easily visible in the fridge. Also, mayo jars are a great way to take pasta salad, or potato salad etc, camping. Label the jars for each person and they can eat and re-close and throw it in the cooler until they want some more. Sorry all my tips consist with camping... but im kinda in that mode since Summer is here tomorrow!
I use my plastic miracle whip jars for water containers for my painting and mixed media work. I also love them to hold screws and nails in the workshop. You can see what's in them and they don't shatter if they drop. They could easily be used to hold leftover paint from house projects for easy touch ups' the relish ones would be good for that too. Squeeze tops can hold anything from mixed up pancake batter to mixed liquid fertilizer for plants to easier to manage liquid laundry soap containers.
I know the feeling, I save also especially clear ones. Peanut butter jars in a couple sizes work great in my husbands workshop. Nail lids up under a cabinet or on a long borad, he can fill them with screws, nails, bolts etc., then screw on to the lids and he can see all at hand. Great for keeping organized.
I also save the clear ones for nails, screws, etc. The coffee cans, I paint and add a circle of magnetic paint for other stuff. Can put a nail or bolt on the magnetic circle so see what's in it.
I use dozens of jars and bottles in my craft room. Lace, ribbons, buttons, beads, a ball of string, you name it, I've got it in a jar. You can dress them up to match with book pages, too. Best thing? You know what's in them just by looking.
I use them for crafts, it easy to see what you have,