Definitely sooner rather than later. We went with DD when she was 6 months and came back when she was 8 months. She was actually really really good and we had heaps of people comment about how quiet she was, so we were lucky. On the way over she was happy to sit up in the bassinet which i'm pretty sure you're not supposed to do, but noone told us otherwise. She sat there and played with toys, ate some food and looked around at everything. At that stage she was sitting up and rolling but hadn't started crawling yet.
On the way back I was flying by myself as well and it was more difficult. DD wanted to stand up the chairs and look at the kids in the row behind us constantly. She didn't want to sit still. It was an overnight flight and we had a bassinet and 2 chairs but I didn't want to sleep with her in the bassinet in case she woke up, didn't want to sleep holding her on my chest and I couldn't get comfortable with her in the baby carrier as the arm rest wouldn't lift up in the seats in the row where the bassinet was.
We did baby food in jars while we were overseas (I found that there was a huge selection of organic baby food with nothing added to it) and haven't had an issue with going back to normal food once we got back. I made sure I took baby panadol and bonjela as DD was teething and tried to organise my carry on bags as much as possible. I found zip lock bags to be extremely handy.
Feel free to ask questions if you want to know anything else