You would actually be surprised how quickly donated blood typically gets used. Most hospitals are constantly short on blood supply, so blood typically doesn't sit around long enough to "go bad." Though, admittedly, do not know if there actually is an expiration date for blood. But yours is probably very appreciated by thankful people who needed it.
To add to your list of benefits to donating blood, it is also very good for guys because it prevents prostate cancer and helps overall prostate health. Yeah, I know, I just mentioned your prostate on idkfa.