Underseat space (or lack of such)
Over the last few overseas trips I've honed my carry-ons so that I have a laptop bag and smaller bag (with my change of clothes, travel mug and snacks) that will fit neatly under my seat. I am too short to practically access the overhead bins during the flight without bothering someone to help me.
I just flew Delta and KLM from the U.S. to Lagos, via Amsterdam, only to find that 3 out of 4 seats I had during the flights contained bulky A/V boxes under the seat in front of them, which left me with almost no usable space to place my carry-ons. This is so unfair! But I thought I'd pass on the info as something to think about when you pack. It doesn't matter how carefully you plan your carryons if you end up with no space to keep your personal items with you during flight.
It seems to be random which seat has the equipment in front of it. Some aisle and window seats are clear, some blocked. (Seatguru.com may have this info, and I'll check it next time I fly.) All I had space for in most of them was my tiny purse (which thankfully I'd already separated from my main bag so that my wallet and such could be with me). I had to do a mad rush on boarding to extricate from my larger bags the essentials such as my travel mug, eye shades and kindle, and inevitably forgot something on each flight.