You can restrict access to all your stuff by setting a single account-wide password. Once this has been set, all your content will be accessible only to those visitors who know the password or have an email invitation.
You can set the password for viewing your account by going to "Settings" >> "Site Settings" >> "Access Control". The account-wide password is an additional layer of protection compatible with all of the other protection settings and as such can be applied simultaneously with them - without the need to change anything else.
When a visitor attempts to access an account with this password set, only a simple prompt is displayed :