I find dumpsters fascinating. What's in them? Why was it thrown away? For example, this dumpster contains a couple of big institutional coffee warmers. Are they any good? If not, are they fixable? Why weren't they given to Goodwill? You also get a view into people's lives because their stuff, normally hidden away, is on display for everyone to see.
Also, dumpsters occasionally contain awesome prizes. I've personally found a Nintendo machine and several games, and I've heard of someone finding a brand-new in-box digital camera. On the other hand, Erin once found a bucket with a turd in it.