Giving blood

I'm giving blood tomorrow morning.  I love giving blood, not so much for the experience itself, although that's not bad, but because of the advice - "Be sure to eat a cookie before you leave."  Take it easy for the rest of the day, no heavy lifting."  "Be sure to rest, eat well and drink plenty of liquids."  In other words enjoy a guilt free day of goofing off.  No wonder I've gone back 70 times.