Sell the stuff to civvy contractors who will remain out there after the departure of UK armed forces. The Chinese might like to use it. They have a fair number of mineral extraction projects ongoing. Or open a scrappy.
The Afghans had rather a lot of Soviet kit left over from the last time there was a mass exodus.
Final suggestion is to put all vehicles in to deep storage at Bastion & leave Bastion guarded by civvy contractors so that the equipment is ready for the next excursion in to Asia.