The Overview: Preperations for hitchhiking across the United States: Map, Food, Money. How long it takes to cross the country. Also, sleeping and navigating the Interstate System.
Hitchhiking across the United States takes 2-4 days depending on how across you're going. West to east is faster than east west: Montana to Pennsylvania is 1.5-2 days; Pennsylvania - Montana 2.5 or 3.
The fastest way to cross the United States east-west / west-east is to stay to the Interstate (highways).
Hitchhiking Map of The United States of America
On my Hitchhiking Maps page I suggest buying a suitable map which denotes rest areas, truck stops, and service stations; along the interstate there are plenty of truck stops selling the big Rand McNally Map Book of the United States, a decent map of each state as well as city maps for the bigger cities. It's the map cross-country truckers use. I suggest you buy it. The book is about the size of your torso and is usually 'on sale' for six bucks.
Food and Money
When hitchhiking in the United States, when crossing the country, I spent $14-20 bucks. Shopping for eats before you start your trip at a local Grocery Store will save you from the food and expense of highway resturants.
The Interstates are numbered and the numbers have meaning:
The Resolve: Get a decent map and buy some food before you try anything darling.