Step 1: Always be prepared for anything... but be flexible.
1) Duct tape- Ok, kinda cliche but true, I've used it to fix swim trunks, radiator hoses and leaky car windows, boats, luggage and many other things, you only need a little roll. ( you can wrap a bit around an ink pen if you like.
2) Tools- somthing as simple as a Leatherman can get you out of a lot of jams. (Think of the dude who was hiking in Nevada and had to cut his arm off with one.)
3) Extra underwear- Yeah you can wash your old stuff in a river or hotel sink or a truck stop bathroom but I really like a clean pair every couple days at least.
4) A map- some times the best maps to have are the ones that states and cities gear toward people with young children. They often have a better list of attractions within a city or state and they are usually free.(and with the maturity level of a 5th grader they are great for me)
5)Backpack- A lot of times I will travel only with a large daypack.
within I can cary a waterbottle, toiletries, a pair of shorts, t-shirt, fleece, rain jacket and even a couple books to read while on a train or plane.
6) Multiple payment options, I always bring a cheque book and cash along with my card, if you run out of cash in the middle of Kansas and need to pay for a campsite cheques usually are accepted whereas there are still many places that do not accept Visa or Mastercard.
7) Flexibility- this really should be number one I can't count the times I've had to change my plans because of rain, wildfires or strange airline standby procedures.