Here's a neat trick that works with some providers: you can include a + sign and an extra string of characters and it will still be delivered to the same address. Example:
user083+some-online-shop@provider.net will receive the mail for user083@provider.net. So you can register with a different email address everywhere yet it all goes to the same account. If your account gets leaked or breached you'll know where it happened thanks to the extra information behind the +.