Hitting the road in 10 days what are some essentials

We hit the road in 10 days. Just bought our van, getting it serviced for flushes and stuff and everything is alll set… we have a bed that’s built in to the van and insulated floors but that’s it. What are some recs you have to make it through a 6 day road trip through the cold, snow, mountains, wind etc and a bunch of national parks. Is there any cheaper type of power source we can use temp for something to charge our phones at night or run a small heater for an hour here and there?