Giving blood is an excellent way to give of yourself to others. One pint of blood can save up to three lives because giving blood means giving three different components that can be used to save a life: red blood cells, plasma, and platelets. And unless you are severely anemic, (which means you should likely not be giving blood anyways) the recovery time after giving blood is quick and minimal. To prepare yourself, make sure you hydrate well and that your iron levels are full, so eat some red meat (but avoid overly fatty foods, which can result in too much fat in your blood and a sample that can't be used for a transfusion) or dark leafy greens.

It usually takes about 24 hours after you give blood for your plasma to replace itself. Plasma plays a key role in transporting important materials from your blood cells and throughout the body. And it is plasma that helps keep your body healthy by fighting off diseases and clotting blood. So the 24 hours after you give blood are crucial to making sure you are staying hydrated and not over exerting yourself. It takes the body about four to six weeks for the red blood cells to replace themselves, which is why it is advised to not donate blood fewer than eight weeks between donations.

The best way to refuel after a blood donation is to focus on drinking a lot of water. And be sure to think about keeping your blood glucose level high, so eating small meals throughout the day is a good idea. Definitely do not go too long without eating and risk a drop in your blood glucose levels. Nutrient-dense foods full of vitamins and minerals are your best bet for helping speed up the time it takes your body to replenish its blood supply: whole grains and fruits and vegetables are great options (dark leafy greens rich in folate, bananas rich in Vitamin B-6, nuts, eggs, and broccoli rich in Vitamin B-2 and riboflavin are excellent options if you need some particular meal inspiration). And just like before your appointment, load up on iron rich sources of legumes, dark greens, and lots of red meat.

Sources
https://www.redcrossblood.org/learn-about-blood/blood-facts-and-statistics
http://www.donatingplasma.org/donation/what-is-plasma
https://www.redcrossblood.org/donating-blood/tips-successful-donation.html
https://www.livestrong.com/article/444113-the-best-foods-to-eat-after-you-give-blood/