WalMart is great, but I find that if I'm not getting a whole lot, Albertson's on Orange Blossom Trail is the more efficient place to stop. It is right off the Greenway, directly opposite the exit. It will cost you a couple of quarters to get off and on the Greenway at that exit, but it's worth it in time saved, IMO. I find that WalMart is at least a 30-min. round trip out of my way if I'm staying in LBV or onsite, and it tends to have long checkout lines.
This Albertsons mostly serves locals; the prices are not inflated. It is not a 24-hr store; it closes at 1 am.