The sponson to the right of the radio operator was used for storage, mostly of ammunition for his MG34. The walls, the ceiling and the floor of the sponson all had stowage points.
Looking in through the radio operator's hatch [2] , we can see that metal trays are fixed to the floor of the sponson. There is an unused area because the hatch opening is halfway over the sponson and the crewman needs the space.
The trays could be removed because they were screwed into welded mounting points. This is the Bovington Tiger during restoration [1] . The paint is not original, but does resemble the original colour. We can see some of the mounting points. (The vertical pole is not an original German fitting.)
This is apparently the first layout of the storage trays. We find this layout in the surviving hull #31. The space between the trays and the wall is for the ammunition pouches that hang on the wall.
The five narrow trays held standard ammunition boxes for the MG34.
The rearmost tray was for MG parts, i.e. the bipod and butt that were needed to use the gun outside of the tank. There was a similar box in the turret.
The Befehlstiger had a different layout due to its extra radio equipment. A first-aid box was put on a new tray in the sponson. (It may have been bumped from under the radio operator's seat.) A new transformer on the central brace occupied some of the space in the sponson. As a result three ammunition boxes were eliminated. This layout is shown in a German drawing of November 1942.
This is the tray for the first-aid box.
At some point early in the Tiger's development the sponson storage was rearranged. We find a new layout in the surviving hull #122, and it remains in force for the rest of the production run so far as I know. The first-aid box is now stored in the front of the sponson in standard Tigers, and only 4 ammunition boxes are carried. The trays are all moved slightly towards the outside wall. I don't know if the Befehlstiger storage was also updated.
Back in the Tiger at Bovington Museum, we can see that the MG parts box sits horizontal, while the others slant along the sponson floor.
This profile shows the radio operator's view of his ammunition boxes in the later Tigers.
In the surviving Sturmtiger at Munster museum all of the items in the sponson are removed, including the welded mounts.
[1] Survey of vehicle 250122, Bovington, by David Byrden
[2] Survey of vehicle 251114, at Saumur, by Jean-Charles Breucque