Measure the pocket, not the lunch box

To fit a lunch box in a backpack side pocket, measure the pocket first, then pick a soft, insulated bag that’s a little bit smaller.

Those side pockets are not all the same. Some are stretchy mesh that’ll swallow a bottle; others are rigid nylon barely wide enough for a phone. So grab a tape measure and check the width and height of the actual pocket. That’s the only number that matters. “Standard backpack” is a myth.

Now, skip the hard plastic or metal lunch boxes. They look nice, but they won’t bend to fit the weird shape of a pocket. Go for a soft, insulated lunch bag. Look for one that’s tall and narrow, not short and boxy. You want the height to match the pocket so it doesn’t flop out when you grab the backpack.

If you’re somewhere between sizes, buy the slightly smaller one. A bag that’s too big will stretch the mesh, stick out, and drive you crazy. And if it’s a little loose, cinch the pocket or attach a carabiner to the strap.

This is a five-minute measurement that saves you weeks of “it almost fits.”