Your yogurt lid is a liar.

The easiest fix is to put a piece of plastic wrap over the cup before you snap the lid back on. The lids on those little cups look sealed, but they’re not. They rattle loose in transit, and the film you peeled off was doing the actual work.

Plastic wrap works because it clings to the rim. You don’t even need to be neat about it. Just tear off a square, press it over the opening, and put the lid on to hold it in place. If you’re out of plastic wrap, a sandwich bag pulled over the top and secured with a rubber band does the same job.

If you’re feeling lazy and the lunchbox is packed tight, you can also just wedge the cup upside down so the lid is pressed against something else. That works surprisingly well, but only if you plan on eating it soon after. For actual forgetting-about-it-until-lunch reliability, the plastic wrap wins.

Your sandwich will thank you.