The BNTO from Cuppow is very simple, but effective. It's a plastic cup that nestles into a canning jar, allowing the jar lid to be screwed on to keep the cup and its contents safely separate from the rest of the jar. It comes in sizes to fit either wide or regular mouth jars; I tested the wide-mouth version ($8.99/2)
The idea is that you can pack your lunch in the jar and keep two components separate. So, salad greens on the bottom and salad dressing on top. Chips on the bottom, salsa on top. Vegetables on the bottom, ketchup on top.
Okay, never mind that last one. Make it crackers and peanut butter, hmmm?
Since the top portion is sealed away from the bottom, there's no need to worry about keeping the jar upright during transport, and the BTNO comes in a variety of colors, in case you need to color-code your lunch.
Besides using this for obvious food pairings, it would be handy for storing or carrying things that aren't quite as related. For example, a snack in the jar, and that medication you're supposed to take with food in the BNTO on top.
This could also be useful for dieters who want to pre-portion their food, or for crafters who want to store related items together. I'm sure the SE readers who suggested this have other ideas, as well.
While this isn't the most earth-shattering product I've ever seen, it makes sense for folks who regularly bring snacks or lunch with them, and who want to get more use out of canning jars they already have.
The BNTO is dishwasher safe.
The product was supplied for the purpose of a review on Serious Eats; this was previously published on Serious Eats.