I suspect it’s a rectangular lunch set from Lock&Lock like this one: https://www.amazon.com/dp/B0089W0SOY/ref=psdc_12900081_t2_B00466I4R0

ETA: I have 2 sets like this and really like them. I just stick the boxes into a larger insulated tote—I lost the bag it came with. These boxes are pretty small however, but you can find slightly bigger rectangular and square sizes on amazon too.