I usually take a zip-topped Lands End canvas carry on bag with my "necessaries", including my small purse, book, pillow (have to pay for one on board these days!), meds, sweater, etc. and a bottle of water purchased on the other side of security.
I am short from knee to ankle and find the seat heights often begin to cut into the backs of my legs in a short while. Therefore I PLAN for my carry on bag to be a foot rest, and pack it "properly" to provide that service.
Jan in VA