Sitting on a table or in lines:
Corn starch and baby powder
Powdered Lactose or Vitamin B powder
Protect the Actor's nasal cavities from multiple takes:
Coat the inside of the straw with Vaseline, so most of the powder gets caught before it gets inhaled
The same recipe for faux-caine will work
Sugar and baking soda,
Retracting Needle or Stunt Needle
Rent or Purchase:
http://www.thespecialistsltd.com/stunt-kit-retractable-hypodermic-needle - I've used their kit before and it worked spectacularly - I highly reccomend this if you have the budget for it
http://www.newrulefx.com/products/retractable-syringe-needle - I haven't tried their needle specifically, but I have purchased other stunt props from them in the past and I am always pleased with the quality of their products and their customer service.
THC free, but otherwise, the real thing:
Buy the real thing without getting the actors high with product bought on legalbuds.com.
Dress that Bong:
Add coca-cola to the water to dirty it up, add crushed cigarette flakes to float in top.
Apparently you can buy stamped sugar pills from a prop house, but I have yet to find the prop house. I'll update this post once I figure it out. Otherwise people recommend Altoids or some other candy with food coloring stamped on it.
Not to ingest:
Krazy glue dropped into a pile of baking soda
Safe to ingest:
Purchase some freeze dried mushrooms from your local asian market
Happy propping everyone!