Patate Marco serves the standard roadside fare: fries, burgers, poutine, etc. Its great place to stop on the way to or from the cottage, especially for the post-party hangover breakfast -- in my experience, anyway...
I really like the burgers, and the poutine sauce is great.
They also have a large ice cream menu and serve delicious milk shakes.
There is indoor seating as well as some picnic tables outdoors. Depending on when you go, you may end up waiting as it tends to get busy with people on their way to or from the cottage.