It depends on technical knowledge of your adversary.
In theory nothing will help you if a violator has physical access to your computer and really wants to steal your data.
For example he can reboot your system in single user mode with root privileges.
You can disable single user mode but he can use live cd or a kind of hack to reset root password.
To protect from booting from live cd you can setup BIOS password (for boot and for settings access), but that also can be bypassed by CMOS data clearing and restoring default BIOS settings.
In addition your system can have running services listening some ports. They also can be vulnerable.
Then he can install special software he need, for example key logger for catching your password and accessing encrypted files/folders/drives.
So the more protection steps you did, the more difficult it can be to get access (more time and higher skills are required). But that is still not impossible.
You can hide your data (if not done yet) in addition to encryption.