Right by the Boardwalk is Walmart. I would strongly suggest going to Publix.  It's a great grocery store with fresh produce and pretty much anything you need.  The closest one to IMFL is:

2419 Thomas Dr (thank goodness for Garmins) 

and it's about a five minute drive.  There is also a Win-Dixie right next to it - but I don't think the produce selection is as good. 

Now, if you want to go out to eat - in my suggestion, these are the best places:
The Boatyard
Great food, awesome atmosphere, and amazing view!
Flamingo Joe's
Not the best view - but if you are itching for a killer burger - this is the place!
Pier Park
Chain restaurants (Olive Garden, 5 Guys Burgers, etc) along with great shopping (including a Target) along with a few other great places to eat with killer gulf views
Mellow Mushroom
(located right at the turn around for the 2nd loop of the run)
Great food (including gluten free options) and a killer patio!
Frankie D's Pizza
Best deep dish pizza on the beach
Finns
Beach version of a food truck - yummmy healthy, fresh tacos etc

Tri/Bike Stores
They do have a pretty killer expo - but if you want to check out the local shops here are a few:
Freedom Sports
Owned by a great local family (ok - good friends of mine as well) -and they also have a tent in the Spinnaker Parking Lot. Need something?  They have it!
Steve's Bike Shop
Have a bike issue?  They will take care of it!  Need a place to ship your bike?  They'll put it together for you!

So - if you have any questions - let me know!!

Next post - other things to do / places to see post race or pre-race relaxation!