That's a big job to self recover.
Yes, empty the truck. Might as well set up camp first, so you're not building camp in the dark exhausted. If needed, scout the local water source. Get on the radio(s) and see who might be able to hear you to send help. Possibly the military.
Now, assuming the box is structural (enough), Id dig under the rear corner enough to insert an air bag. I carry one (never used; only tested) and if that was my rig, I'd have a bag with sufficient capacity.
Then the fun starts. You'd need to rig to the trees on the underside of the truck side (so you can right it) and I can't see those clearly in the photo. You may have to daisy chain rig several trees at the base. Then, using the non-existent and/or PTO driven winch (powered by the non-running engine) start the pull as the bag is inflated. This would probably require a block ahead of the truck, to limit the side pull on the fairlead (yeah, the one not present on the rig) which would be anchored to... The Pull-Pal maybe?
Better to have MANY vehicles and hands. Do a direct pull on the roof (straps wrapped around the box, attached to the frame, same as a semi-trailer righting when it rolls off highway) supplemented by the airbag. Multiple trucks. Each truck anchored to the tree bases behind them. To limit speed I'd perhaps block it (double-line pull) for the trucks rolling the truck back over. Then a third truck (or pair of trucks) pull it forward onto solid ground once it is upright.
Self-recovery on a rig that big/heavy requires a lot of training beyond what a typical trail guy might have. And the equipment necessary is a lot bigger and heavier as well.
Just for a bit of perspective, I put my 110 nearly in the same situation with a drainage ditch on the side of the "road" where the grass was all cut flush and the ditch was not visible (although it was my own lack of focus that caused me to go in there) and it took a 101FC anchored to a 90 to get me out of that. Another, similar, but in deep snow filled ditch, we dug out as much as possible and relied on a tractor-trailer to get me out of that (might have been the Alaska highway in Canada but I'm not certain now). I wasn't coming out otherwise, and it took a good 50-75 feet of pulling before I could get traction to get out of the ditch. That truck shown probably weighs twice what mine does...