Why are donuts sold in wax coated bags?
Because doughnuts contain large quantities of fat in them. fat soaks through most materials so the bags are made of plastics, so the fat and grease doesn't soak through
Heroin is sold in different packaging. On the street its sold in "bags" (tiny folded wax paper) and a bundle is 10 bags. Most people cannot afford a gram of heroin. A gram of heroin is usually a bundle so a bag would have a 1/10 of a gram in it. Heroin is distributed by neighborhood and city wide drug dealers.