I've been donating blood for decades. It's one of the few morally unambiguous things you can do these days. In addition, I have many friends who cannot donate for a variety of reasons so I try to take up the slack. I usually donate at work but, because of the summer, they skipped a cycle so I checked at the ARC to see about walk-ins.
West Madison's ARC center wins the prize for the quickest donation EVER! Granted, it was slow day over there and I know the ropes but, I was out in 45 minutes! After quick, friendly and professional attention, I was sipping OJ, eating a cookie and walking out with a free loaf of Panera bread (on Thursdays and Fridays) under my arm in less than an hour.
I won't suggest that you'll get through that quickly but, if you can, donating blood should be a thing. Do it. Save lives!