Osprey 22 inch ozone 46 liters @ 4 lbs. I could have gone smaller but when I went to Chicago or NYC in the winter I needed a bit more room for an sweater, rain shell and or my Patagonia Das Parka
For 5 to 6 day business trips
Book hotels that have irons in the room and coin laundries,
Slip on dress shoes worn on plane
One sport coat or suit jacket worn on plan or rolled, no hangers or folding and packed in luggage.
For most meetings since my industry is biz casual, the same jeans I wear on the plane can be worn to meetings. If I were presenting to a big customer in Manhattan or making a formal presentation to big group, I would bring wool slacks rolled, and one tie.
No more than one or two changes of underwear (including smartwool T shirt). I would use Dr Bronners hotel shampoo to wash socks, boxers every night
Sundries in zip locks
One extra dress shirt
Gym shorts, swim googles, lightweight shoes and one cotton T shirt for gym
I sometimes checked my bag instead of rolling it aboard, it was usually 16 lbs or so
I also carried the smallest Timbuktu backpack with an 11 inch Mac Air inside. I never went the one bag for everything route since I needed a laptop bag to carry to customer meetings and make presentations.