It's not too bad at 5 months old. Are you leaving on a night flight? Plenty to drink of course, and standard toys, a few new toys. If weaned some snacks (bread sticks are good as they keep baby occupied). Whatever you need for sleep (favorite blanket or soft toy). In any case I would bring a small blanket (might make it easier for you if she falls asleep and you want to get off the plane). Carry everything in one backpack, in which you will also be able to fit your handbag (you don't want to carry more than one bag, and wheely bags are really not practical as you can't push the buggy and pull it at the same time). DSs loved baby books so I had a few of those.
Nappies/wipes obviously, a bib or two, change of clothes (i would bring two changes top to bottom, including a pyjama).
I'm afraid jet lag you just have to go with the flow and if it's possible for you to sleep as she is asleep during the day, even if it means that it will take you longer to get over the jetlag yourself.
I fly to Canada and it's normally an afternoon flight to go and night flight return. Last time I did it on my own with my two boys, who were 2 and 3.5. It's hard but feasible.
Make sure you have a drink ready for take off and landing as she might cry because her ears will pop. Drinking will help her getting over that bit.
I also remember having sheets of stickers which kept my DSs busy for ages at take off. I just put stickers on their hands and on my hands and we just played with that.
Do you have a fabric sling? if it's a small one it might be useful. I used to have a ring sling and it was useful to get on / off flight.
Also, check the allowance for a buggy some airlines only take small (umbrella fold) buggies. Let me know if you have any other questions I'll do my best. BP