I do my divin' in the early morning; I bring gloves, a little head lamp, and I know what dumpsters to hit. Depending on what day it is, I'll bring in Odwalla protein drinks, pizza, fresh sandwiches, and so on.
It's hit or miss according to weekly business cycle: Monday - Weds = low waste. Thurs - Sun = high score. Know at what time the dump trucks come through. For my route, it's early Mon and early Thurs.
The Trader Joes and all those are ideal, but don't discount a plaza with 3 or more businesses located. Often times, the property is owned by one property owner - who is out of the area. Typically, the property owner designates and allocates dumpster bins for each business.
So each bin will have their own designated waste in it. Go through the bins to get an idea of where things are. Employees will typically keep up habit, so if you see a big score on one day, chances are high something similar will be there next time.