Tent, sleeping bag etc in the car along with bike. Stove, coffee bags, muesli, oat milk for breakfasts (first breakfast, anyway…) One set of riding clothes and one set of regular clothes for each day – who cares about weight when it’s all getting chucked in the car!
I have 2 collapsible totes, one has my wet/cold weather riding gear, helmet, etc in; the other holds tools, bits’n’bobs, locks and so on. They’re what I chuck in the boot when going mountain biking anyway so they’re always ready to go.
Car has a jump start power bank in the boot, so I can charge my phone/lights/Bolt from that.
I could be on the road in an hour or so after deciding but usually I’m planning 2 or 3 days out and looking at the weather forecasts (don’t know why I bother, it usually ends up raining…)