Given the right tools and supplies I would have used a helmet or hard hat to secure the box to my head. But without that available I had to come up with some other way of keeping the box on my shoulders and not slumping forward or back.
I had some bubble wrap but not enough to secure the box well. I realized that I could use zip sealing plastic bags filled with air to create pillows inside the box.
These turned out to be VERY hot but I wasn't going to be able to wear the box for more than 20 minutes or so at a time so given the resources it worked out well.
One gallon bag on either side and one in the back and a roll of bubble wrap below the mouth opening that i could sort of brace with my chin worked out very well. I just used some packing tape to secure the bags and bubble wrap to the opening at the bottom of the box.