Here are some tips on what to eat before and after giving blood, which should help prevent any wooziness.
Don't give blood when you're very hungry. Try to schedule your donation so that you can eat a healthy meal no more than 4 hours beforehand.
Don't donate blood if you are eating a very low-calorie diet for weight loss. If you're dieting, ease up a bit and eat slightly larger portions of protein foods and vegetables the day before and of your donation.
Immediately afterward, a piece of fruit or small cup of yogurt would provide some easily digested sugars to keep blood sugar from dipping--and be a healthier choice than cookes. Prunes or prune juice are high in iron and would be a particularly good choice.
Drink plenty of water before and after donating blood to replace those fluids. (Blood is mostly water).
Make sure to eat foods that are high in iron in the days before and after donating blood. The form of iron in meat, poultry, and fish is the best absorbed. If you're a vegetarian, prunes, prune juice, and blackstrap molasses are all good sources of iron.
stay healthy..:)