You can add a plus sign to the end of your email address, and then you can set up a folders in your email that coordinate with that. For instance, say you open an online account with Wells Fargo. When you sign up, give your email address as "firstname.lastname@example.org", then in Settings, set up a filter. In the From box, add in Wells Fargo or your chosen bank, in the To box, put in your newly-created email@example.com address, and then set the filter to put in a folder titled "banking." You can also use this technique when you sign up for something and send their emails to you directly to the trash!