First off, if you have not stumbled upon the website for The Kitchn yet, go do so right this minute! I'll wait.
I love, love, love them. Seriously. I've learned more from their tips, recipes and reviews than any other site on the web.
One of the tips I especially like is their "Quick Tip: Freeze Caramelized Onions". Most of us probably prepare dinner in a bit of a rush, just having rolled in the door from work, tired, hungry and not wanting to fuss with complicated steps. I generally don't want to have to wait for things in the evening, so I take short cuts or skip steps which means dinner isn't always a blow-your-socks-off gourmet treat.
One day I came across a super deal on a ginormous bag of onions at the market, and I thought I'd give this tip a try. So I spent a Saturday afternoon crying and cutting onions while watching romantic comedies on tv (we'll blame the tears on the onions... that's my story and I'm sticking to it). Once chopped, I threw my trusty cast iron skillet on the stove on a med-low setting, oiled the pan and threw the onions in (in batches, overcrowding the pan will make it take much, much longer than necessary), sprinkled with a bit of salt and let it sit. Stir every now and then but otherwise go about your business. It will take a while, but letting them get to the rich, brown caramelized stage slowly will really be worth it (and that says a lot coming form someone as impatient as me). Plus the house just smells divine... something about cooking onions is such a comfort smell in the kitchen. Probably less so in your linen closet.
Once all the onions are done, I put them in a bowl and let them cool completely. To store, I just put them in a large freezer bag, press out the air and seal the bag, then flatten the contents to one even thickness and put in the freezer. They take up no space at all and I can just take a spoonful out whenever I need it. The Kitchn article suggested in muffin tins or ice cube trays as well, though I find the bag method works fine for me and takes up less space in my crowded little freezer.
It's a fair bit of work to start, though not a bad way to spend a dreary Saturday afternoon, but once done they give such great flavor to soups, stews, sauces... anything that strikes your fancy! No tears necessary.