Originally Posted by
fanostra
I use a packable duffel bag from REI that I picked up a few years ago for that very purpose. Its very small so its a no-brainer for me to toss it in my main bag on trips. As you can imagine a bag of that nature doesn't have a lot of structure to it so I'll often put my laundry in here an any pick-ups along the way into my main bag. That said it has been invaluable to me. Even used it in place of a daypack on a hike, slung over my shoulder like a messenger bag with passable results.
Not sure if REI still sells the model I have - seems to be listed as no longer available
http://www.rei.com/product/748504. But this one is close:
http://www.rei.com/product/778792
Looks like this Micro Duffel has a pretty mediocre strap though in contrast to mine (which is average but serviceable to start with). You can probably find others from eBags or elsewhere.
These are good, but I really had in mind something larger. I'm not attached to the duffel, but I sort of expected a duffel to be the closest. The micro duffel and day pack are much too small ~1000 cubic inches. The stowable duffel is closer, but still pretty small ~2600 cubic inches. These would be solid choices to stick in a carry on bag. But I'm looking essentially for a second checked bag. Any thing bigger? For comparison, the basic eagle cargo duffel is 3600cubic inches in medium and 6700 in large.