These solutions are way overcomplicated. By far the easiest way is to go to System Preferences ->Users & Groups->Login items tab and click the plus and select the app you want to start.
Also in System Preferences ->Users & Groups you can select Login Options and select your user for automatic login of that user. THERE IS NO SECURITY RISK TO THIS UNLESS YOU GIVE OTHER PEOPLE PHYSICAL ACCESS TO YOUR MACHINE!
Anyone with physical access to your machine can boot off an external drive (or various other methods of bypassing your login password) and have access to all the files on your hard disk. The correct answer to your computer's security is not to have your computer nag YOU to enter your own password every time you walk up to it, instead it is to lock your room! Has the added benefit of not allowing your 3 year old to rip out the keys on your keyboard, spill orange juice on your mac pro, and other such things.
So remember, login passwords are only for shared work areas/environments where your computer is somewhere everyone else can walk up to and use - something you should never do with your home PC in my opinion. If you have proper physical security, the login password is just a waste of your time and should be disabled, it provides almost no security at all.