If you're in a situation where you have to walk 400 miles to find safety, I don't think pepper spray is going to do much for you in the way of defense. That stuff barely works (if at all) when you can quickly spray an attacker and then run for help and call the police. That's not going to be the case in the scenario described. I would take an extra loaded mag for the .40 over some pepper spray. The .40 should be in a holster on your hip too, not buried in the backpack.

Actually, I think the OP has done a lot of good thinking and researching on the BOB. Planning to walk 400 miles is maybe a bit over the top in terms of realistic expectations though. Especially with a 6 year old.