When I previously donated blood at the DRK, not only did I always get a Bockwurst&Brötchen along with a selection of beverages (water, cola, coffee, tea, etc.) but also a little gift bag containing a variety of little food and drink items, like a banana, an apple, little bottles/packets of fruit juice, (fruit/chocolate/etc.) joghurt cups, all in all maybe ~5-7€ worth.