I like these threads, they give me ideas. I don't have a box, but do have a compartment in the cargo area.
The things I carry that I've actually used: leather work gloves, X lug wrench, jumper cables, battery jump box, flares, little air compressor, cheap set of tools, some 8" zip ties, small roll of TP.
Also carry 2 16 oz pepsi bottles with washer fluid, heat sealed in a mylar bag. Haven't had to use that yet, but here in the fall/spring it's possible to have so much salt on the windshield that you need the stuff to see to drive. I use soda bottles because they're tough and I've never had one leak. The rest of the stuff that I didn't use I stopped carrying with me.
Up front I carry a spare set of glasses, a towel, roll of paper towels, rain jacket, sometimes a hat, snow brush in winter, flashlight, knife, tire gauge.
Used to carry a chain or strap. These days I don't, not sure why. I used them twice, but more than 20 years ago, so maybe that's why.
Used to carry a sleeping bag, back when I drove less reliable vehicles and I didn't have a 2m radio and cell phone with me.