Hi
I flew with my 6 month old DD last year (alone) and again when she was a year old (with DH). We traveled to the states both times and it was about 24hours worth of travel so some may relate and some may not...but thought I would share all I learned!
I brought the buggy both times. As we had a lay over I found it very useful...however the second time I checked the buggy in with the bags as I had DH and she was walking. I knew we would need it on the other end for the trip but not in the airport. Up to you though as if you have a delay it is handy to have a place they can nap and you can have a little rest yourself.
I got a sling for the trip and I loved it! I was able to walk on the plane with her when she was restless and also was able to have hands free for security and paperwork. Also I felt better having her attached to me in the busy airport but would find quiter places to let her run before we got on the flight.
Bring extra set of clothes (everything down to socks) for you and DD as she may get sick in flight either on herself, you or both.
Bring more wipes than you think you will need. I was anal about wiping the seats, seatbelts, tables, and everything she could touch as she was at the stage of putting everyting in her mouth. Also eating on the plane is a messy experience...but something she will enjoy.
Make sure she has a bottle or something to snack on or a dummy during take off and landing even if it is just a rusk. I made sure of this for my DD and she did not have any ear problems at all.
Bring some pain meds and teething gel just incase. My DD decided this was the perfect time to pop in those molars.
Bring toys and books she loves. Don't bring anything noisy...and I found that Crayola Colour Wonder markers and paper was an amazing purchase as the pens are clear and you don't have to worry about marking on the plane or putting in mouth (non-toxic but still watch). This kept my DD occupied for ages...and I was able to color lol
Bring any formula pre-messured in a container and buy water after you get thru security. Don't bring cartons or pre-made bottles as they will make you open the cartons (which then you can't carry with you) and will make you drink from the bottles.
Bring more snacks than meals as my DD only wanted to snack both times and didn't eat one single meal.
If you are staying with friends first off, ask if they would mind getting a few things for you. I did this with family and they got nappies, wipes, formula and various snacks my DD loved before we arrived. This made things easy in the first few days as we didn't need to go restock and DD was happy to have familiar foods when we got there. I also did not have to pack loads of nappies.
Pack light. You don't need as many clothes for DD that you think you will. Also with friends you will hopefully be able to do a wash.
Hope that helps and I will post more if I think of it lol