Rule #1: Respect Continental Scale (Pick One Coast or Corridor Per Week)
The continental United States spans 2,800 miles (4,500 km) and four main time zones. For a 7- to 10-day trip, commit to one cohesive region: the car-free Northeast Corridor (Boston, NYC, Philadelphia, Washington, D.C. by Amtrak), the California Coast & Yosemite, the Southwest Grand Circle National Parks out of Las Vegas, or South Florida & the Keys.
Rule #2: Lock In ESTA ($21), Park Permits & Open-Jaw Flights Early
Book an open-jaw ticket (e.g., into Boston BOS and out of Washington IAD, or into San Francisco SFO and out of Los Angeles LAX) so you never waste a vacation day backtracking. Apply for your official $21 ESTA at esta.cbp.dhs.gov and check Recreation.gov 60–120 days out for timed-entry park permits.
Official sources & further reading
Rules, prices and schedules change. Confirm details here before you travel: