I have my trailer hitch ball mount in there, it fits pretty well and the straps hold it securely. Wrapped it with a rubber mat to keep the rattle noises down.
When I bought my truck, it originally had a fire extinguisher mounted with both straps holding it. It looks exactly like yours but mine mounted to the side whereas yours will lay down. But I guess you can use it for whatever you like.
I believe they came factory with either a Med-Kit or an extinguisher.
Yeah it's where the JBL subwoofer is, so in non-JBL models it's just storage.
It can be removed by trimming a couple of plastic pieces and the JBL speaker grille clips in. I would assume it's just used as storage so they didn't have to make two different molds for the entire part.
Tow strap, hitch, hot hands, spare pair of gloves, extension cord, various other items. . .flashlight. . Berreta 92-FS. Just depends on what I'm doing that week.