It doesn't take much to get started. There are a few reasons for this:
In Blue Highway, the author described his functional gear like this:
I had what I needed for now, much of it stowed under the wooden bunk:
In modern terms this might be:
1 sleeping bag and blanket;
1 Coleman cooler…;
1 Rubbermaid basin and a plastic gallon jug (the sink);
1 Sears, Roebuck portable toilet;
1 Optimus 8R white gas cook stove (hardly bigger than a can of beans);
1 knapsack of utensils, a pot, a skillet;
1 U.S. Navy seabag of clothes;
1 tool kit…
If you want to charge phones or a laptop, it is easy to pick up a lithium "power station" and charge it when you stop for a sit-down meal, coffee, or anywhere else with an electrical receptical. This type of unit charges very well from an outlet, ok from solar, and poorly from a ciggy lighter socket unless you are driving.
A backpack and extension cord come in handy for smaller units; you can put the battery in the backpack and run the extension plug to the wall. No one needs to know you are charging a pack.
Larger units will be able to power CPAP and similar devices.