I donate regularly, they have various types of donations such as plasma, RBC, platelets, etc. It's just a question of how much time each one takes to donate, and how much you have to wait in between donations.

My grandpa donated his whole life and the karma was returned to him in the end when he needed transfusions in his dotage, so that is my motivation.

Do it, at the very least you'll get as many juice boxes and bags of cookies that you could ever want.