Just the thought can be daunting ( I remember beforre my own child listening to the screaming and crying and thinking the cherubs were being tortured !) However I have flown with my daughter 9 times and she is not yet 2! We rarely have too many dramas if you make sure you have a few essential items!
1. A couple of familiar smallish soft toys.
2. Their favourite book and a new book
3. A couple of small new toys or borrowed from a friend.
4. Your essentials bag - nappies, wipes, plastic change mat etc...
5. FOOD! Pack into small sandwich bags - small amounts of- sultanas, rice crispbreads, etc..If taking foods taht need to stay cool such as cheesesticks, small yoghurts etc het a small insulated cooler bag and put a small icebrick in there and use these snacks first.
6. The airlines are pretty good if they know you are travelling with a toddler or small child and if there are any spare seats, will put you next to it so that you have plenty of room! Don't be afraid to ask if you can move if there are spare seats.
The airlines usually supply a lap belt for your child- it attatches to your belt so that they sit on your lap- I have found that this is where my little girl is happiest during longish flights anyway! If your husband is travelling with you - takes turns!
7. I know that some babies and children have difficulties with the change in air- pressure and their ears can hurt- I was still breastfeeding once a day up until recently and letting them have a breastfeed as you take off and land avoids this! If not still breastfeeding- try a bottle of water or milk as the swallowing reflex relieves the pressure on the ear drums.
I always took my port- a -cot with me as I found it was familiar and we never had any problems at our destination getting her to sleep in strange places. Without it....well lets just say, no-one had much sleep!
Good luck, hope the trip goes well- sorry it is for such a sad reason.