I bought this a few months ago because I wanted something to use as my personal/under seat bag that I also didn't have to lug around on my shoulder if I checked a bag, and I love it so far: https://smile.amazon.com/gp/product/B071G2D5MM/ref=ppx_yo_dt_b_asin_title_o07_s00?ie=UTF8&th=1
I usually pack stuff into a medium or large sized packing cube that fits perfectly inside with space for other items, it has 2 side pockets and a good size front zip flap with pockets inside, it's a wheel luggage bag, and it has the strap on the back to slide over another rolling luggage handle!