I use this one.
Arxus Travel Lightweight Waterproof Foldable Storage Carry Luggage Duffle Tote Bag https://a.co/d/ii5l7cA.
Sorry, I don't know how to paste links. It's on Amazon. It is very lightweight and folds into a very small shape. On the other hand, because it is so thin, it doesn't pad anything inside. I usually just use a large purse on the way to a cruise and pack this for the return trip. The purse fits inside for the return trip and there is still a lot of room left.