Use a Password Manager
You might think that all of your passwords for various websites are safe and sound, but once someone has physical access to your Mac, it's really easy to see what all of your passwords are if you have the web browser save them.
In Chrome, all you have to do is go into the settings and select Manage Passwords. From there, you can get a list of all of your passwords that you have saved.
Instead of this, use a password manager like LastPass, which will not only store all of your passwords in a password-protected virtual vault, but it will create random passwords for you; even you won't know what your own passwords are. All you need to know is your master password.