I've never had trouble flying with stuff for DS (now 15 months). TSA has never questioned me about it, and with flight delays, I would always plan to have extra stuff anyway. There is no way you can buy formula at most airports, and if you're stuck on the plane for hours, you have no option either. Of course, they will not let you have enough for the entire trip.
One option too is the dry formula packets - we had some we received as samples when DS was born, and since he was generally BF, we never used them except when travelling. But, try before the trip and see if your baby is ok with the powered stuff. The benefit of these is they are very portable, very lightweight, and all you need to do is add water and shake.
For me, I was generally OK packing for trips with DS without planning trips to the store. You can estimate the amount of diapers and pack those (or if you'll be gone long enough - order on Amazon.com and have a large box shipped to your hotel - maybe you can have the cans of forumla shipped too?). Overall - I could carryon a diaper bag and small tote with DS and my stuff, and check 1 bag with DS and my stuff, including diapers, formula, etc. for a 1 week trip.
DS at 6 mo was very easy at Disney. It was Oct - so the weather was easy. He was very portable, happy to nap in the stroller or in my baby carrier, and happy people watching, etc. He loved the characters at that age - I have wonderful pictures of him laughing with Pooh and Eeyore (by 13 months he was scared of them). We used Baby Care on all trips - it's a nice place to change a diaper, let him crawl, or nurse/feed a baby (or take a break in AC if it's hot). I had a nice lightweight, semi-reclining travel stroller for him, and that was all we needed.
Overall, DS has been at 6 mo, 8 mo and 13 months - and 6 mo was the easiest.