I am like a nickel of weed rolled in a doobie - I'm a little twisted
A nickel is $5.00 worth of weed (which isn’t all that much).
When you don’t have enough weed to fill the paper, you twist it (the central pun of the line — Royce is “twisted” aka nutso). Royce is also referred to as “Nickel.”
To help improve the meaning of these lyrics, visit “Writer's Block” by Royce Da 5'9" (Ft. Eminem) Lyrics and leave a comment on the lyrics box