In my car, I have two pilot-case type luggage.
One contains tools, oil, etc ... for the car itself.
The second one contains gear for the passengers : water, dehydrated meals, alcohol stove, psk, change of clothes, light hiking shoes etc...
If I have to leave the car in a hurry, I will grab the second one and walk a bit, with the case in hand. Then, I'll take time to stop, open the pilot case, extract the small (and cheap) pliable rucksack I keep in there, transfer the gear from the case to the backpack and go on, hands free.

Now this is OK because of the limited volume of my gear.
A big BOB for a whole familly may not be so easy to transport.