We have done several trips back to the UK and back to oz again. We learnt our lesson after thr first trip, as our daughter was only 9mths old, she slept in bassinette but if you hit turbulance you have to take them out. This made for a very overly tired baby on the leg out, the return we didn't have turbulance. Our 2nd trip we chose to do a one night stop over in Singapore on route over and this made for a better trip for all. Our daughter was aged 19mths then. We took playdough, crayons and paper, but dependent on who you fly with they also provide activity bags. Our best purchase was a portable Dvd player, we took about 8 dvds with us and whe watched those when she grew tired. Our return leg we stayed in Hong Kong for one night and almost a whole day, which really helped with jetlag.
Since we always pack our own little food snacks, such as crackers, sultana's and fruit. Our daughter suffers terribly with her ears, so we also take ear defenders which help. If you have never flown with your little one before, I suggest you invest in these, as having their ears hurt during descent/ascent is excruciating for them, you and others.
I suggest stop-overs of at least 12 hours, so your little one can stretch legs, run around and burn off energy. Take night flights too, as they will sleep for 4 + hours if you do!
Good luck!