We took an 11 hour flight to Oahu 2 years ago. This time we have a stop just to be able stretch.
I made up a little bag with eye drops, hand lotion, lip balm. and asked for water. I did seat exercises about every hour I was awake. (making your toe go in small circles etc.) Stood up and stretched. I also wore "flight socks" I do suggest them.
My trip over was fine however coming home was another story.