Most of the people I wheel with that cary that much spare parts just bring 2 rigs lol.
I cary spare shafts, hardware and items but the main reason I trailer is if I had a bad enough breakage like a ring gear or locker I can load up and go home. I'm not a race team, rock bouncer and not carrying a spare jeeps worth of parts to go wheeling.
Granted we aren't traveling that far to wheel or having the benefit of wheeling for 4 days at a time. That might change a bit if I did but probably not much these days.