Each pack comes with 2 straps to secure it to you board should you choose to.
Flip your accessory pack over and thread the straps through the attachment system as shown.
Be sure to lengthen the straps first before looping them
Attach the pack to the board by securing using using the buckles.
Tighten the straps by pulling at the ends and using the strap loops to fasten the loose ends.
Repeat for the other side.
You would only need to do this once or when you switch over to a new board.