That box was for stowage of rations. These vehicles carried a crew of four people when in service and these men were fully equipped with enough equipment, gear and ammo to stay out for a couple of days at a time.
Space was a treasured commodity and everything that was necessary had its own stowage space.
This shot was taken whilst 6RAR (5 RAR wore a yellow ribbon laced around their giggle hats) was loading to go out on an op in 1967
https://www.aulro.com/afvb/images/im...11/04/1245.jpg
See this site for a further general description of the vehicles: What Makes This a Gunbuggy ? - REMLR
Regards
Glen

