I'm not a local but I spent a season there a couple of years back, hopefully this stuff still applies...
Bread is like 10c cheaper per loaf at Overwaitea if you buy the unsliced loaf and then put it through the slicing machine yourself. Go figure. They also have samples at the deli all the time so go tax them. These are kinda ski-bum season-length tips though, I guess.
There's a little butchers shop roughly opposite the library, beside the bank with the red and white logo. Can't remember what it is exactly. Their minced beef is a million times better than Overwaiteas and it's cheaper. Their sausages are also pretty awesome, if it's still the same then they do a big ass bag of them for about $10.
Food is generally cheaper at the huge supermarket at the opposite end of town to the ski field. Only slightly though. If you have a car then it's worth driving down but it's a shit of a walk if it's -30 and you've been skiing all day.
The Brick House (is that what it's called?) used to do a ribs night that was pretty cheap and the ribs are damn good.
Oh and try to avoid getting on the booze. It costs way, way too much. I think jugs of Kokanee at the Grizzly Bar (in the main lodge, upstairs) during happy hour weren't too bad though.