As a more direct answer to your question: If I'm leaving my car to strike out on foot, I have two basic scenarios in mind.

1) It's time to go RIGHT NOW. In that case I'm grabbing the bail-out-bag I built for that purpose, and then beat feet. No time for integration; if I didn't duplicate that function then I better not need it.

2) There's at least two minutes. For this case, step one is to STOP: Stop, Think, Observe and Plan. Maybe I dump the nonessential contents of my laptop bag and fill it with essentials (because my laptop bag is the most comfortable backpack I've ever owned). I could probably do that in a minute or two. Maybe I'm not going too far, have people with me, or can make multiple trips, and then I can bring all of the ridiculous contingency gear I've filled the trunk of my car with.