I did 10 hours with DD2 at the age (the worst child ever TM.., agreed by all!)
I was so nervous about it I was having sleepless nights.
I didn't let her eat or have her milk all morning (flight was at 10.30) and let her run around the Virgin lounge to her hearts content. I booked seats upstairs so less people and more room, plus a little cubby by the side of the seat for everything... Do this if you can!)
I was pretty much the last person on the plane, and let her moan for as long as it took to take off. Then I have her her milk, and when she finished it, a 'that's not my book' which she threw about every three minutes for about half an hour.
I took enough food (snacks and baby food) and toys so that I could feasibly give her something every half hour if need be. I only gave something new when she started to moan, and the very best thing was a Disney magazine I let her just rip to pieces. Then she fell asleep (because she was knackered from running around the lounge etc) for about 5 hours! When she woke up I have her the iPad and then when she started to get bored I gave her a dummy with it and finally, chocolate buttons, filled out one at a time for about an hour!
It worked, it was hard by we survived 
On the way home, she slept The Entire Way. Red eye all the way for me in the future!!