Just did same journey with my 2.5 yr old to St Lucia. Premium prob has seat back TVs which amused my Dd. Also lots of little snacks, drinks, - assume plane food will be rubbish - new little books (try Waterstones), tiny doll and teddy, colouring. We did walk up and down the plane a lot of times. Take spare clothes for you and them (spent several hours covered in wee...) and cool stuff to change into before you land.
Loads of sticker books on amazon eg http://www.amazon.co.uk/Maisys-Easter-Egg-Hunt-Sticker/dp/0763620718
Little pots of playdough with accessories for cutting it up and squishing it through things
If you can fit one of these in your luggage it might be worth it. It kept my 2 year old DS happy on a recent flight and for many restaurant meals on our last holiday http://www.elc.co.uk/toy/super-scribbler-blue/