I use them for freezing my chicken broth after roasting or baking a chicken (or turkey, ham, whatever leaves juice behind). I always leave enough room for expansion and have found that when they've broken (maybe once or twice), they don't shatter into tiny pieces, but rather large, easy to remove fragments.
I also use them for draining off grease after browning hamburger or cooking bacon. I cannot pour it down my drains for fear it will build up and clog them, so I put them in the jars and then throw them away when full.
I've also made gifts out of them by adding a small strand of Christmas lights, filling with potpurri, then topping with a doily threaded with a colorful ribbon to tie off and make a 'lid'. When the lights are plugged in, the aroma is heavenly
Oh, and never underestimate keeping some on hand for summer firefly catching, assuming you're in an area that gets fireflies
My kids also like to keep mini bug farms going when they catch something neat or interesting. Just remember to poke small holes in the lid or your bugs won't last very long.