Without doubt, the most important tool we use when out metal detecting (other than the metal detector itself) would have to be the digging tool!  Whether you are detecting at the beach, in a grassy field or in the gold fields, a purpose built shovel or scoop can massively increase the amount of finds made by increasing target recovery speed.
This may sound obvious but when it comes to metal detecting, a large amount of time is spent simply swinging the detector and scanning the ground. If things are going really well and you are finding a lot of diggable targets then an even larger chunk of time could be spent digging and recovering these detected targets than scanning. To help minimise the amount of time digging for targets it is essential you have the best digging tool for the job.