Closest is Goodings in the Crossroads Shopping Center. Not the cheapest, but closest and you can get your McD's fix there.
12521 State Road 535
Lake Buena Vista, FL 32830
Telephone: 407-827-7300
Here is tha address of the one already mentioned and it must be new since we were last there in Dec 2005 ....
Wal-Mart Supercenter
3250 Vineland Rd, Kissimmee, FL
(407) 397-1125
If you continue on 535 you will come to US192 and at that junction on the left is a Publix:
Publix
2915 Vineland Rd, Kissimmee, FL
(407) 396-7525
If you turn left onto US192 and go a couple of miles there will be another Walmart Supercenter on the right just past Medival Times. This is where we have gone in the past.
Wal-Mart Supercenter
4444 W Vine St, Kissimmee, FL
(407) 397-7000
What we normally do is go to Goodings if we just need a thing or two. Otherwise we go to the Walmart on W. Vine and if we don't get everything we need, we stop at Publix on the way back.
We always go the back way where there is less traffic and hopefully I won't miss a turn here. Out of FW parking lot turn left onto Vista Blvd and follow that road until you get to Live Oak Lane and turn right (there should or used to be a Child Care Center on the right just after you turn onto Live Oak Lane) and then another right onto East Buena Vista Drive and follow that and turn left onto Hotel Plaza Blvd (just past the DTD bus stops on the right). When you hit 535 go straight across to Crossroads Shopping Center (Goodings) or turn right onto 535 to get to the Walmarts/Publix I listed above.
If you want to follow the previous directions given by Brad and go to Goodings just turn left onto 535 vice right and go under I-4 and The Crossroads will be on your right at I believe the first SL.