Yo bro...its me Oliver!

1. Bakeries are a great place to dumpster dive. The food is generally just baked goods so it's not gross or a health concern like meat would be.

2. Half Price Books gets more books than they can handle, and though they say they donate the books, they really just throw them in the dumpster out back. Though they usually aren't the best quality, they can be read, donated, or at the least used for firewood
I'm on a roll

3. If you live in a city and have extra cold weather gear that you no longer need, keep this stuff in your backpack or car. When you see a homeless person give them your old stuff. It's better than dropping it off at a shelter because you can be sure that it got to someone in need. The same works for non perishable food. 
This really beats doing homework.

4. Write positive or inspirational little notes and hide them around. I like to put them under keyboards in computer labs or tuck them like bookmarks into library books. Random interesting facts or jokes work well too. Fake gossip or rumors can be fun too, someone may believe they got some inside information

5. Start doing graffiti.