You can log in to your account automatically by checking 'Remember me on this computer' on the log in page.

When you check the box and log in, Remember The Milk sets a cookie to remember you when you return to the site from the same computer. The cookie lasts for two weeks, after which time you will need to log in again. To disable the cookie, just click on your avatar at the top of the page and select 'Sign out' in the menu.