One of the larger ones in my city. 95% of the time the "tool section" is just **** and random junk (broken stuff, single brake pads or struts, water heater hoses, curtain rods, plastic boxes, generic screwdrivers, 30 year old corded drills, etc.).
The trick is to just go often because you never know what you might find. It's a little over a mile from work and next to a grocery store, so I'll walk over, grab a yogurt and do a quick sweep through the Goodwill before heading back. I am time limited, so I have gotten pretty efficient, lol
My method is go straight to the tools, maybe glance at the boxes and electronics, go check the toy section for Lego, and walk through the bag section on my way out. Whole thing is sub-10 minutes, often closer to 5.
I have found an old Bahco/Sandvik saw, diamond SK ratchet, old Snap-on bit driver and metal case, Wiha bit ratchet set, Igarashi pliers, assorted vintage screwdrivers, a sealed Lego set, a purse, and probably some other stuff I am forgetting over the course of a year and a half or so.