Only 5% of the eligible population donates blood every year. Are you one of those 5%?
If you're not sure about your eligibility, check the Red Cross's blood donation eligibility guidelines. I have acquaintances who've told me, "Oh, I'd love to give blood, but they can't take my blood because of X," but when I've looked up X I've often found that it doesn't actually prevent them from giving blood. Let's take two common examples:
Blood pressure, high: "Acceptable as long as your blood pressure is below 180 systolic (first number) and below 100 diastolic (second number) at the time of donation. Medications for high blood pressure do not disqualify you from donating."
Diabetes mellitus: "Acceptable two weeks after starting insulin. Medications to lower your glucose level do not disqualify you from donating. Those who since 1980, received an injection of bovine (beef) insulin made from cattle from the United Kingdom are not eligible to donate. This requirement is related to concerns about variant CJD, or 'mad cow' disease."
The bottom line is that you shouldn't rely on what you've heard from other people or intuited yourself to determine your eligibility, but instead should check with your doctor or local blood donation organization. After all, you don't want to be missing out on all those free cookies and juice.