Speaking from experience - remember that there is no changing area in those tiny airplane bathrooms. When I traveled with my 3 month old daughter, I had to change a dirty diaper in the floor of the gally area. And this was 5 years ago, I think the rules have changed some since then! Wet diapers are easier to deal with, you could change those while she's laying on your lap. If she does have a dirty one, you might could lay her head in your friend's lap and change it, if you don't mind showing her hiney to the person sitting on the other side of you! Also, take something to tie the diaper up in. It could quickly stink up the whole plane otherwise. ;)
Also, as far as the gear goes, you need to think about getting all of this equipment to and from the airport. All of that is a lot to try to man-handle out of the airport and to a rental car or to the curb for a pickup. Maybe your friend's dad could find a neighbor or someone from church that could let you borrow a pack and play? Maybe even a car seat? The travel system is a good idea, except that more than likely you will have to check the car seat at the ticket desk and just use the stroller in the airport. I've never been allowed to take a car seat onto an airplane without having to pay for a seperate seat. Check into the rental ideas from the other mom. That's a GREAT idea. If you're squeamish about rental beds, take your own sheets. That's what I would do.
As far as what to take for baby on the plane, you'll need your own water to mix formula for bottles. Take some bottled water in addition to pre-filling the bottles. You never know when I bottle may be needed to soothe baby girl. Also consider sealing the baby food containers in a plastic bag just in case of a leak and to have a place to put the empty ones and the dirty spoon once you're done. To keep her entertained, buy her a few new toys just for the plane ride. If she gets antsy or fussy, you can pull out one of the new toys and keep her entertained. If she hasn't seen it before, it will hold her attention longer.
Most importantly, be prepared that she just might have a total meltdown somewhere over Georgia and you'll be stuck with it. Travelling with a little one isn't easy, but prepare as much as possible for every scenario and you'll be better off! Good luck!