Off the top of my head, I'd suggest the Publix on SR-535.
Taking the south exit from MCO you'll travel on 417 to exit 6. The exit ramp will put you onto SR-536. Get over to the left lane and at the 2nd (I think) light, make a left onto SR-535. Pass the LBV outlets on your left and you'll be approaching US-192. Publix will be in a shopping plaza on the left - you'll turn at a traffic light before 192. I can't recall the name of the road but it is BEFORE the Burger King which is in the same plaza as the Publix.
To get to WL from there, go back the way you came and turn left onto SR-536. Stay in the left lane and once on WDW property, follow the signs to the Magic Kingdom/Magic Kingdom Resorts.
There is also an Albertson's and a SuperTarget just off 417 at the Orange Blossom Trail (17/92/441) exit but I prefer Publix.