Matador - Freefly Packable Duffle Bag - Luggage

Lets get the negative out of the way first, there are a few different packable duffle options out there and most are cheaper than this! If you're just after a packable no-frills duffle, this is not it.
BUT, if you're after a packable duffle for travelling, this is the best option you could get. It packs down small, it's waterproof, it fits within the carry-on dimensions for all airlines and most importantly for us, the compression straps also work as luggage pass-through straps. This allows us to slide the handle of a wheeled bag through the straps and not have to carry the duffle separately.

From my own personal experience, we (family of 4) travel carry-on only a lot,. So far we have used it to store warmer clothes when we have reached our destination (and on the plane if there's space overhead). We've also used it when travelling between destinations to increase luggage capacity. And finally, its saved us money with budget airlines as we havent had to pay for an empty case outbound that we know we're going to fill when we're at our destination.