I use GlassLock containers that came in a set from Costco. You can also find them in those Asian markets individually. They look similar to the Lock-n-Lock glass models, with tops that have 4 hinged latches and a rubbery gasket inside (bento box style). This set had several round, square and rectangular sizes. I got tired of plastic that got damaged and stained in the microwave, figuring that glass would be the safest and cleanest, despite some weight and fragility. Most of them I just use daily in the kitchen. They've held up well, no chips and no hinge failures. The gaskets should be removed every so often for cleaning, as liquids do creep under the gasket and grow black crud (probably mold).

So far (many years), they have not leaked at all, placed sideways in a padded bag in my panniers for a 2 mile commute. While I don't recall taking any really liquid food in them for this trip, I do put thick fluid stews and such in them, no problem. I think if I had really liquidy soup, I'd use my Thermos/Nissan soup container and preheat it.

Perhaps there is some magic/trade secret to this technology where some work, and some don't.