» What it is: A blowfish of a polyester bag that zips shut to less than an inch thick for easy packing in your luggage.

» How it works: It’s the rare traveler who doesn’t come back with something from a trip, whether clothes, shoes or maybe a bulky rhinoceros carved out of soap. This forces you to buy another bag for the trip home because you were already maxed out with one checked bag. That’s where the backup bag comes in; it’s thin and light enough that it doesn’t consume precious space in your primary bag. It swells to 19 by 13 by 10 inches, so you can use it as a carry-on or as a second checked bag.

» The good: I tried this on a trip to Italy, and it spared me the last-minute scramble for an overpriced second bag. I used it to carry home most of my dirty clothes, freeing up space in my other luggage. But I also encased a new stove-top espresso-maker within the clothing, hoping to cushion it against the big bruisers in the plane’s cargo compartment. All of my most cherished purchases went into my regular carry-on. The backup bag sustained no damage despite an obvious drubbing.

» The bad: The espresso-maker’s box, however, did take a beating despite my clothing cushion. Fortunately the espresso-maker itself survived. This is a soft-sided bag, so don’t count on it to cushion that blown Venetian glass in a cargo hold. Use it to carry crushable items as checked baggage or as a roomy carry-on. Unfortunately, the shoulder strap does not detach for stowing as checked baggage.

» Cost: $29.29 at Amazon.com

–Ross Werland, Chicago Tribune, www.chicagotribune.com.