This GI is 'humping' the SC-300 / BC1000 man-pack radio usually reserved for infantry platoon headquarters.
This radio set was known as the 'walkie-talkie' while the hand-held SCR-536 /BC611 was nicknamed the 'handie-talkie'.
Radiomen usually carried a lighter weight personal weapon... sometimes a 1911 Colt Automatic .45 pistol or, more commonly, the M1 Carbine as is shown here.