If you don't want to take your data with you, you can wipe the entire disk and all of the data will be gone. All your files will be deleted forever. Even if a user can't see the information, it will be there, it just cannot be read.
But it takes a bit of work for those with basic skills. There are software programs that will do it for you. The downside is that you cannot take back your data. If you don't want anyone seeing your information, use physical methods to wipe the disk.