"Lunchfest" is when you wake and bake and then are too lazy to make or go get breakfast, so you wait till like 1 or so, till the hunger builds and then you pig out stoner style.
A meal taking the place of both breakfast and lunch. Unlike "brunch" which is usually a hearty, planned affair in a restaurant, lunkfest usually consists of fast food or whatever food is lying around the house, and is usually the result of sleeping into the point where eating a separate breakfast and lunch would be impractical.