It seems that there are different answers to this question since the folks working in the Bakery often make exceptions (or mistakes) but ...
In Sept 2008 Main Street Bakery was our favorite Breakfast spot!
We were told that our CS credit would give us:
1 large breakfast item (breakfast sandwich, french toast loaf, large yogurt/fruit parfait)
1 side (pastry or large fruit cup)
1 large drink (large bottle of OJ, milk, etc not the smaller single serve size)
Others on the DIS have quoted differently, but this was our experience on several visits during our trip... YMMV
Hope that helps!