How to Avoid Vacation Disaster

Bring a cellphone for emergencies
If you're going on vacation to unplug, do not take this as a requirement to have your phone turned on and on your personal at all times. You just need a phone for emergencies, and it doesn't even have to be your phone. You can purchase a throwaway phone for about $15 and keep it in your car just for emergencies. I recommend having a phone that you can dial any number on (and not just 911; you'll see why in a second).
Have phone numbers for roadside assistance and addresses for local hospitals
If you're a member of an auto club or any organization that provides roadside assistance, have their numbers handy at all times. Also, look up the hospitals in your travel area and keep the addresses and phone numbers in your vehicle. If somebody gets food poisoning from eating at that five star restaurant that your coworker told you was sogood, you don't want to be hunting for a phone book.
Have a GPS
I believe the invention of the GPS alone has eliminated the majority of arguments that occur between trip-mates. It also has made sightseeing a lot more pleasant because you can free your mind from the nagging question, "How do we get back?" If you don't have a GPS, get one. It is one of the best investments you will ever make and will pay for itself in saved miles and less stress.

Bring cash
If your credit/debit card numbers happen to get swiped while you're on vacation and you suddenly have no way to pay for anything with plastic, cash will be your friend. Even if your identity remains intact, many local merchants will only accept cash, or will surcharge you for using a credit card. Cash is quick, easy, and anonymous. (And most vending machines still don't take credit cards.)

Protect yourself with personal self-defense items
Make sure you check the laws in your travel area, but bring the highest level of protection you're comfortable with. If you own a handgun and know how to use it, it is the best form of protection. However, a taser, mace, or even pepper spray is better than nothing. Exercise vigilance and be on alert, especially at night. Just the fact that you are alert, aware, and prepared will often keep a potential predator from bothering you.