Create a second email account, and use that when signing up for stuff. Configure the second email account to auto-forward to your real email account. That way you can check its emails without having to login to it.
If you start getting spam at email@example.com, just drag them into your spam folder. Eventually gmail will learn that everything sent to firstname.lastname@example.org is spam, and you'll stop getting it. (The second email account method has an advantage in that you can simply stop forwarding it and stop using it immediately. You don't have to wait for Gmail to learn.)
In my case, I own my own domain and my email goes through my own doman. So I create a new email alias (kinda like an auto-forwarder, but happens at the email server level) for every site I sign up for. So I have email aliases for email@example.com, firstname.lastname@example.org, email@example.com, etc. If I start getting spam, I know exactly which site sold my domain name out, and I simply have to delete the alias to stop it. (FWIW, Microsoft is the only major company which has sold out the email address I gave them.)