I currently have a bag that zips 3" x 3" flat. It's just a little too small and doesn't slide onto a luggage handle. I probably should have said large tote, slightly smaller than what people use for weekends. We pack light and carry on our luggage when we are outbound. Occasionally we buy stuff (wine, coffee, linens, olive oil, Burks) and can't quite fit everything into our luggage so sometimes we need to check the carry on (especially when we have liquids, of course) We need a small bag to put overflow items. I also think something like that could double for a picnic bag, or spot for raincoats/umbrella on drive days. I just need something that takes very little space that's why I was thinking nylon.
I did look at the Arxus bags, which look promising, and the search also turned up some alternatives that might work.
I was curious what people that have similar needs use.