Small flat pocket on the side for treats, poop bags and I fit in some flat folded paper towels in case there is a leak (from my dog). It fits well under any of the seats of a Boeing 737-400. The first two photos were taken on a brand new 737-800 on Southwest in a 3-aisle-3 configuration, I’m sitting in the window seat.
https://www.amazon.com/Sherpa-Travel-Approved-Carrier-Medium/dp/B000633ZOY

