Yes, its his gas mask canister and entrenching tool. Seems the model makers at Palitoy made the prototype more accurate. Anyhow, the actual figure and later Red Shadows has this equipment molded onto his back.
I wished they'd made his helmet removable. Used to have one of these fellas....when I was a kid that is! Its like a monkey pissing gold now trying to find a loose one! Nevermind!
P.S. If I recall Jonesy posted pics of other trade catalogues....what happened to the pics? Any chance of a re-upload? Im particularly interested in seen the Action Man stuff.....