If you are already going to be on 417, just stay on it to exit 6 which is the exit for Downtown Disney. You are on vacation - the extra dollars spent on the tolls on 417 will be WELL worth it.
50 has lots of lights, lots of traffic and lots of accidents. 417 on the other hand, has very limited traffic and a speed limit of 65mph. Yes, you'll pay tolls but the convenience is worth it.
For groceries, there is an Albertsons and a SuperTargel just off 417 at the Orange Blossom Trail (17/92/441) exit. Easy off and easy on. Alternatively, there are a couple of Publix supermarkets in the area (one is very close, I believe, just past the Shrine and the Premium Outlets) and a Winn-Dixie just a little ways past Hotel Plaza Blvd. on 535.