Complex sentence: Tony decides to have some but his skins are in his back pocket so Sid has to get them where he then inadvertently release the cars handbrake causing the car to roll into the harbour.
Split into simpler sentences: Tony decides to have some but his skins are in his back pocket so Sid has to get them. While getting them, he then inadvertently releases the car's handbrake causing the car to roll into the harbour.