Your passport is essential. Without it, you won't get past airport security, let alone out of the country and into another one. Check ahead of time to see whether or not the country where you are visiting requires a visa. If you do not have a visa, you could be rejected by immigration officers when you arrive you the country you are visiting. It's a good idea to make a copy of your passport to store in another suitcase while you travel, too.
While not required, it is a good idea to purchase travel insurance, in case of any medical or travel-related problem. Keep a copy of the policy with you.
Many countries run appliances at 220 volts. Your appliances, if designed to run at 110 volts, could suffer complete failure by burnout if you do not carry a voltage adapter with you. Besides adapting to a foreign country's voltage, you'll have to adapt your country's power plug to the visiting country's power outlets. You can purchase this converter separately, if your electronics already have a voltage converter in the battery, or you can purchase a device that converts both voltage and electrical plugs.
Although this seems obvious, you need to pack clothes for the country in which you are traveling. Besides considering the weather, also consider the modesty and style of your clothes. If you are going to a country with more traditional, modest cultural values, you will want to wear clothes that do not offend the people and make an effort to fit into your surroundings. If you blend in because you look culturally appropriate, pickpockets, thieves and terrorists will have a harder time identifying you as a tourist, and therefore a target.
Bring at least a small phrase book, if you are unfamiliar with the local language. Even though many people in tourist shops of major cities will be able to communicate in English, it is appropriate and respectful to try to speak in the language of the country you are visiting. If you can translate road signs, menus and other forms of written words, you will have a much easier time with traveling.
While travelers' checks are still a very good way to bring money to foreign countries, you can also bring your local currency to exchange at a foreign exchange booth, or you can exchange currency at home for the type you will need while traveling. ATMs are popping up all other the globe, too, so it is often possible to insert your bank card and pull out money in the local currency. Check a current edition of a travel guide to the country in which you will be traveling to see if they have ATMs available.
Immigration officers in some country will require you to show your return ticket upon entering the country. Keep this handy and safe in your luggage at all times.
