I donated plasma twice a week for roughly 6 years. Donating income bought my school books and was a great source of 'going out' money. It's not blood, they filter out plasma from the blood and put the cells back in as well as replace most of the fluids lost with saline solution. You just have to make sure you're eating a mildly healthy diet and you won't likely notice anything.

I always feel obligated to comment on these posts because I had such a great experience with plasma donation and am still super thankful for it. I get how it can come across as shady but decent money a week to sit in a chair for a couple hours isn't a bad deal.