The wireless button lets you to tag the important moments of a game from a distance.
You can order an extra button for your assistant and you can connect up to 8 buttons to your iPad.
Since the buttons are carried a lot in games, they are easy to lose, therefore, it's not a bad idea to have a replacement button.
Using these lenses will help you capture a wider area of the field. You just need to clip them on top of the iPad's camera.
The wide angle lens gives you a 110 degree viewing angle. It won't be enough to cover the whole field, but it will keep a great image quality.
The super fisheye gives you a 238 degree viewing angle. It will cover the whole field, which means you don't need to have a cameraman at the game. In large outdoor fields, however, the quality might suffer from the lens's distortion.
iPads are not waterproof so in case you want to film your games in the rain, you will need a waterproof case.
These cases will seal your iPad hermetically and keep all water out, while allowing you to film (with sound) and use the touchscreen.
They also serve as a protective covers in case you drop the device.
These adapters let you connect your iPad to a TV or projector, so you can do team presentations.
The Lightning to VGA adapter will allow you to connect to older projectors with no transfer of sound.
The Lightning to HDMI adapter will allow you to connect to newer projectors and TVs.
Check which one you have at your club house.
Beware of buying adapters that are not from Apple's official store or retailers.