First of the Day
First of the day, is actually the first drink of the day. Usually this is centered around, if in College, one waking up and instinctively grabbing beer instead of breakfast first. In other circles, this runs along the lines of taking your flask, mickey, 26er, or other bottles of liquor and swigging it - in those cases it can occur anytime during the day, preferably earlier from 8:30 AM - 1:00 PM. Continued drinking to follow.

However this term does not only apply to those who like alcohol, the term can also be used for drug use, wake and bake is synonymous with first of the day. Basically any intoxicating substance can be applied, though as a general rule alcohol is the main one considered.

From Easy Rider:

Jack Nicholson's character along with Dennis Hopper's and Peter Fonda's have just been released from the county lock up. Nicholson pulls out a mickey of Jim Beam and states,

"Here's the first of the day fellas. To ol' D.H. Lawrence."

He then swigs the Jim Beam and in a knee-jerk reaction lifts one arm and moves it like a chicken with a seizure. He makes a sound that echoes within the group,

"YA!!!!! ni-ni-ni-fu-fu-fu-gaahhhh... Indians."