reserve tank
The lingering powder in the back of your nasal cavity that drips down your throat and just keeps giving you an extra boost after you've already been blowing lines.
"Damn! I thought I had snorted down all of that adderall, but I keep tapping into my reserve tank."
"Good thing I still have some blow left in my reserve tank. I'm all out of lines."
"Good thing I still have some blow left in my reserve tank. I'm all out of lines."