If you already own the original LCD BacPac or Battery BacPac, both are compatible with the new HERO3 cameras.
The Wi-Fi Remote, LCD Touch BacPac, and the new Battery BacPac are compatible with the HERO3 camera and the HD HERO Original or HD HERO2 cameras.
You do not need a Wi-Fi BacPac if you have a HERO3 camera since the HERO3 camera has built-in Wi-Fi. You will need the Wi-Fi Remote or the GoPro App if you want to use the HERO3 camera's built-in Wi-Fi though.
Please note that there is however limited compatibility for the LCD Touch BacPac with the HD HERO Original and HD HERO2 cameras. The LCD Touch BacPac touch interface does not work with these cameras, but you can control it just like you control your original LCD BacPac. The camera's Shutter button is used to select menu options, and the Power button is used to cycle through menu options.
The Battery BacPac also has limited compatibility with the HD HERO Original and HD HERO2 cameras. Pass-thru charging is not supported, which means that you'd need to charge the Battery BacPac and the HD HERO camera's internal battery individually.
The current 3D HERO System is NOT compatible with the HERO3 camera.