This one is a really simple one, I just didn’t know about it.
When you’re signing up for an account at something like Twitter, you can actually change your gmail address. So instead of putting in your account:
You can put a plus sign (+) and additional text:
If you ever get email from Twitter from that point on it will have the “+twitter” in the email letting you easily filter out emails. But what’s even better is that if someone like twitter were to give out your email address for spam purposes, you can see who it was who sold you out!