I switched a few months ago from an underseat backpack to a small wheeled carryon that has fit under the seat on every flight I have taken since, including at least 4 DL CRJs. I can no longer carry bags on my shoulder nor lift a bag into the overhead, and needed something small enough for underseat and light enough for me to manage, with enough room for my laptop/tablet, chargers, meds, a change of clothing, toiletry bag, etc. This one fit the bill perfectly:

IT Luggage IT-0-1 Second Generation World's Lightest 2-Wheeled 16" Carry On

http://www.amazon.com/IT-Luggage-Gen...d%27s+lightest

I might add that I ordered and returned at least 7 other "under-seat" carry-on options that were just too big to fit under the seats on the regional jets. This IT bag works like a charm!

P.S. It also comes in black: http://www.amazon.com/IT-Luggage-Gen...ref=pd_sim_a_4