Packing a cigarette with marijuana after removing some of the tobacco. Useful for smoking in public areas, since it appears to be a normal cigarette. Usually packed into the cigarette using a pencil (which fits perfectly), hence the term.
Let's pencilpack a couple and go smoke on the white house lawn.
When you scotch-tape pencils together lead-to-eraser style with the intent to create a longer and more lasting pencil. This technique can, and sometimes is, used for many pencils at the same time, creating what many call "The TruePencil-Centipede".
"My pencils are all so short I decided to make a Pencil-Centipede, and it lasted the whole school year!"