We had a really good lunch last summer at the Griffin Gastropub in Bracebridge. It's in back lane, so intakes a bit of work to find it. Lots of Muskoka brews as well. The original Wabora is also in Bracebridge if you are looking for Japanese food. Of course, there's also Marty's in Bracebridge for ice cream and pie.
Milford Bay trout farm has great smoked fish (and a pond to fish in, if you like).
Gravenhurst farmer's market (Wednesdays) was better than anything I found in Toronto.
There's a honey vendor at the farmer's market that had pretty amazing wildflower honey.
Muskoka Brewery is in Bracebridge - their (new?) Summer Weiss beer is getting some attention.
Cosmo's Smoked Meats (find them at farmers markets) has great sopressetta.
Keep your eyes peeled for church bake sales - sometimes fun.
There are some dinner & lunch river cruises in the area - nice way to dine...
Lots of berry picking in the area.
Do some jet skiing and follow it up with a cheeseburger at Clevelands House!
Be sure to make smores.