...jam jars have interchangeable lids. Instead of keeping a hodge-podge of glass jars for storing leftovers, we save and reuse just those two types. Thus we have containers for large and small amounts of leftovers, and only one set of lids to match for both. The Bonne Maman jars are fairly pretty, and the Gefilte fish jars are nice once the labels are off. They're good for storage because they go straight down--the mouth of the jar is about the same diameter as the jar itself.
Our sugar bowl is a Bonne Maman jar with a red and white gingham lid.
Leftover tomato-lentil sauce, or green split pea soup, goes warm into a big glass gefilte fish jar and seals well enough so that it can be left in the fridge while we eat something else the next day. I think soups and sauces keeps better in glass jars than they do in plastic ones in the refrigerator.
Glass is easier to clean. Not good for lunchboxes, of course.