The biggest mistake in family road trip planning isn't what to pack — it's underestimating how much space it all takes once it's actually in the car.
A minivan or a larger SUV is worth the upgrade for trips longer than a couple of days with kids; the extra cargo room reduces the daily repacking headache significantly.
Soft-sided bags pack more efficiently than hard suitcases in a trunk, since they flex into gaps rigid luggage can't fill.
Keep a small bag of essentials — snacks, chargers, a change of clothes — within reach in the back seat rather than buried in the trunk. It saves a full unpack at every stop.