"Half-step Mississippi Uptown Toodeloo" is a name for the way Jerry plays guitar.

"Get yourself a powder charge/and seal that silver mine" suggests a plan to close off some pathway of pleasure with a spectacular, ultimate act of violence, conceived perhaps not in a moment of clarity but at the height of the fever of intoxication, when images of the evil of digging into one's brain are crowding in, and it seems that only some form of selective suicide could solve the problem all at once, like maybe taking a massive dose of the object of pleasure itself, like, this one last giant powder charge may finally do the trick.