This inflatable foot/arm rest is incredibly dorky (you feel SO SILLY blowing it up on the plane!) but it's been amazing for when I was traveling internationally for work frequently. It's my #1 tip for anyone on long flights- because it inflates you can custom-rig it into unique spots for a specifically shaped arm or footrest. I end up using part as a footrest and another part as a pillow against the window. https://www.amazon.com/Flypal-Inflatable-Blow-Up-Cushion-Fli...

The other key item I bought is this giant inflight blanket that compresses down to nothing but makes you so cozy and gives privacy- it also has a pocket for your earbuds and phone: https://www.amazon.com/gp/product/B006LR6ILQ