Well I'd vote for Boots - High leg (gardening, bondu bashing, and all round outside mucky jobs) and the old blue denims. For some reason the green denims never felt the same!
Honourable mentions to the DPM jacket and trousers, and the knife/fork/spoon sets.
With regard to the PT undergarments for the WRAF, when I was on GST1 it was pointed out by one of the blokes on the course that these items were "B" stores, that is they had to be exchanged for a new pair rather than just discarded. The conversation then worked around the subject of disposal of the returned items, with the suggestion that there were boxes of used pairs probably in a hangar at Stafford awaiting someone to suggest what to do with them!