Hey, cool. Your trip caught my eye because my wife, a couple friends and I did this in 1976 (Bike Centennial) as independents.

We flew from our home town of Seattle to Washington DC and proceeded westward from there. We were in our 30s then.

I concluded that we didn't need a sleeping bag until we got west of the Rockies. East of that was warm, really warm, compared to Seattle.

Washington DC and the first couple of weeks west of there just about killed me. I had no experience with heat and humidity prior to that.

You can go really light. Bug and rain protection is your primary concern. I'd go with one of Henry Shire's tarp tents or something similar to that.

A credit card is mostly what you need.