We just got back our son is 14 months, we also travelled with him at 6 months (we took him to the FL Keys) anyway we drove to FL from NJ the last 2 times and it worked out well, we tried to plan around his schedule and plan most of the driving through his sleep and nap times when he would wake up we would just stop at a restaurant or mall let him get out for a while and get back on the road, it took longer but we were fine. The first trip we brought his pack and play but this past time we got one from Disney's hotel, it was fine, in good condition, I brought his pack and play sheet from home so he wouldn't be sleeping on linens that didn't smell like his.
FOr this trip we used the portable DVD player more than I thought we would. My son loves Elmo and we couldn't find sesame street on the tv's at the resort.
If your son is already drinking milk and he drinks whole milk it is available everywhere, 2% is almost non-existant but you can get 1% a lot of places including the resort. We bought an inexpensive travel fridge (plugs in in the car and the hotel room) it holds about a 6 pack and we picked it up for $20 it was well worth it because at the value resorts you still pay $10/night for a fridge. If you are using formula I reccomend the powder and it mixes up easily anywhere with bottled water.
Baby Care centers are great...they have them in all of the parks, I think the nicest one is in Epcot, right before you go into Mexico, they have great changing tables, high chairs and anything that you may have forgotted, they are sponsored by Nestle so I think the formula is Carnation, they did have Gerber baby food we forgot ours in the room one day we paid $2 for the 2/pack of Applesauce (which is twice what I pay at the grocery store)
Bring dish wipes or dish soap as you will need to wash bottles and/or sippy cups I brought the dish wipes and a bottle brush, I just wrapped the wipe around the brush and cleaned it worked fine. We brought a pack of 64 diaper which worked out to be about right.
Bring your own stroller, it will be really difficult to rent one in the parks there is a bit of walking to and from and this way you can do other things outside of the park area. Also, your baby has enough new stuff around him to adjust to, I think it is nice for them to have the security of some of their own things.
Sorry this was so long, I could go on forever.
Nicole