Ziploc 70935 Small Square Food Storage Containers 4-Pack | BPA-Free Plastic Meal Prep Containers for Lunch, Leftovers & Snacks | Perfect for Home, Office & School Organization

The reviewers who have been unable to make the lids stay on aren't doing it right. Like them, I tried to snap them down at the corners, which you can do after they'v been in use for a few times, but the instructions ("When all else fails, read the instructions") do say to push down on the CENTER of the lid. Works every time. I like these because they have steeper sides than other designs, so they slip deeper down into each other, which makes it possible to store more of them in the same space.