This Saturday, the Ben and Jerry's on SE 36th and Hawthorne is teaming up with the Red Cross to host a "Pints for Pints event": they'll give a free pint of ice cream to anyone who donates a pint of blood between noon to 5pm. Since starting the event in 2008, the Hawthorne Ben and Jerry's has given out about 800 pints of ice cream, which is about 53 entire humans worth of blood.
Important note: Anyone who tries do donate blood can receive the free pint. Check the eligibility requirements before heading over, but be aware that they rule out sexually active gay men ("Are a male who has had sexual contact with another male, even once, since 1977?") and people from West Africa.