the kind that come with a new uke... but is longer used. for example, my Rebel came with one of those nice but ugly IMO gig bags that will never be used since I got a case for it.
I'm with you on the Rebel gig bags. Great ukes, really ugly bags. I've had two. The first one had a vinyl finish and I sold it with the uke. The second one had a terrycloth-like exterior. I didn't think the original bags could get worse but they did. Why would you cover a gig bag with an absorbent material?! My coworker has a nine year old daughter who was learning to play the uke and her gig bag was little more than a dust cover so I gifted the Rebel bag to her. She loved it!
Gig bags can be had almost everywhere at a decent price so trying to sell a Rebel bag isn't really worth the effort since there will be so many better looking options. (and shipping would make selling it even less worth while) The best bet would probably be to donate it or hopefully you can find a friend or acquaintance or a little girl who will take it off your hands or give you a nominal amount for it.
On topic: I only have one redundant gigbag, that lives in the corner. But yeah, if I had many I might try to sell them for a nominal amount on the local second hand marked webpage. Pickup only, I would not go through the trouble of sending cheap items like that.
I bought a bunch of ukuleles at an auction once and they dumped a dozen low-quality gig bags into the box with the ukes as a "bonus" (also the "concert" sized hardshell cases I bought were actually sopranos but I digress).
Anyway, one of our local elementary schools has an ukulele club and I've been meaning to stop by and see if they'd take the bags as a donation. I figure they'll either be incredibly grateful or they'll point to a closet, packed full of gig bags. Then they'll release the hounds.
The one I got with my Leho tenor is great, seems like semi-rigid because it’s so well padded and made with rip-stop like strong nylon. I took it on plane, tour bus, car and the use never suffered any injury. Maybe it only misses some neck support but really I can’t believe how sturdy it is being given with such a low price instrument (sounding great and with a good set up “straight out of the box” for the price btw). I don’t know if they sell it separates from ukulele though, it’s black with orange binding.
Unfortunately I don’t have any spare gig bags but I would give it away locally to someone who needs one/schools/bands etc.
I use them to store other things. I use one to store some old flutes and whistles - they are too cheap to use but might have a use with the grandkids. Another holds a variety of cords.
But the best use for one I’ve found is as a carrying bag for my music stand. my stand fits nicely in an old kamoa tenor bag. As a bonus itcan also hold my iPad and some sheet music.
A "surplus" Pukana La soprano bag (they are a bit oversized) holds a music stand with another one converted to a ukulele stand. Great for hotel rooms. I try to nest smaller bags in larger bags for storage.
I took a couple to our local uke club and offered them to anyone who wanted them. A few new ukers had no case of any kind for their ukes and were happy to take them.