IME experience add about 1 gram for the plastic wrap on the handle and about 10 grams for the cardboard on the string bed.
Keep in mind, on most racquets you can easily snap the cardboard off the stringbed , weigh the racquet, and then snap the cardboard back on a again. But if you do this, remember that you are weighing the racquet STRUNG. The UNSTRUNG weight of the frame could be anywhere from 10 to 20 grams less depending on the string used and the density of the string bed.