Well - your trip from Tampa to OKW will likely take you 1.5 hours (or more - with the way traffic is on I-4 these days), so you won't be wanting to stop too early - unless you have a cooler.
I would wait and stop at a grocery store once you get to Disney - there are MANY in the nearby area. Do some searches on the boards for directions to local stores. Some have told how you can fax your orders to a local Albertsons before your arrival - and they'll have it ready for you.
But - if you seriously are wanting to stop along the interstate - there aren't many. There's a Publix at the new King's Crossing (is that what it's called?) development - which isn't too far west of WDW. For the most part, any other stores are just too far off the interstate to be worth the trouble, IMHO.
Have a great trip!