Mass is roughly in kg. That is, a mass of 0.5 would equal about 500 grams.
Drag and angular drag are more arbitrary values (related to air resistance).
The higher the drag the more the movement of the quad slows down.
The higher the angular drag the more the rotation of the quad slows down.
Generally speaking the most important thing is to get the feel right (as opposed to trying to get numbers to directly match reality).