Your mobile phone/camera phone
Lately everyone has a cellular phone to carry around; this became more or less our way of life. Also, don't forget that is a safety device we carry on for emergency. If you have the Internet activated on your phone is even much better. Camera phone can be great for instant takes, you just never know what you run into or who.
Your airfare tickets
If you fly, you definitely want to make sure you have the paper tickets or your confirmation flight number and time of departure. Or, you should make sure you have the info on your phone.
A photo ID card/passport
Most likely in the States you identify yourself with your driver license; however, if you travel overseas, make sure you have your passport with at least within two months expiration date.
Copies of your wallet/money purse belonging
We got so hooked to use Credit Cards, everyone does and it make sense; for traveling purpose, have a separate folder with copies of all what you carry in your wallet including your passport. in case that get stolen, you will have the proper information to report. also, have a list with those cards issuers phone numbers.
Make a list with your itinerary, route and an emergency contact person that is not traveling with you. Also, list any medication you are on and are critical to your well being, in case something bad happens.
These are must have of course, besides your luggage with your belonging. Have your police station informed of your time out of the property and provide them with your contact information while you are out of town.