I have a good friend who does extreme couponing to supplement her income. I have actually even seen her get paid to buy things due to retailer miscalculations.

Her garage is stocked with such things as laundry detergent, deodorant, various cleaners etc which she sells on Facebook and Craigslist. It does involve a decent amount of time, but she has it organized with folders and does the couponing purchases while shopping normally.