Although a lot of information is available on the Internet, a good guidebook, such as The Lonely Planet or Rough Guide, is helpful for the general overview it can give you about a country or city, its history, and important customs you should know about where you're visiting. Guidebooks also provide useful information in times of an emergency, such as hospitals with doctors who speak English, and the number and address of your embassy or consulate. They also tell you about local attractions and hotels and which areas to avoid, and provide maps to help you get around.
If you'll be visiting a non-English speaking country, it's a good idea to get a phrasebook with a dictionary, like the Lonely Planet Phrasebook. It's small enough to fit in the back or side pocket of a small day bag or purse. A good phrasebook will be organized by situations, such as "meeting people," "ordering food," getting around" and many other situations in which you'll find yourself. A good one will also provide a crash course on grammar, pronunciation and the alphabet, if different from ours. It's wise to take a little time before arriving to learn how to read the language and a few basics to get you to your hotel.
Regardless of your budget, don't skimp on shoes, especially if you plan to visit lots of museums or do some hiking. Few things can ruin an outing more than sore feet from cheap shoes. Buy a good, brand name pair and it will last you the duration of your trip, even a long one. If you'll be walking a lot, look for lightweight shoes that are breathable and dry quickly. A pair of comfortable sandals, for warmer climates, will allow your feet to cool down while your shoes air out or dry out, and you can also wear them in the shower.
A good bag is worth its weight in gold. Look for durable ones that can withstand being tossed around by indifferent baggage handlers, dragged on the ground and battered by the elements...and are able to carry everything you pack. If your traveling for business and staying in hotels, a lockable, hard bag with wheels is a smart choice, as it's easy to carry and will keep the contents from getting crushed and wrinkled. If you're getting off the beaten track, look for a pack that's comfortable to wear, has several pockets for easy access and durable zippers that you can lock. A water-repellant material is also a wise choice.
No matter how long you'll travel, less is better. You can always wash socks and underwear in a hotel or hostel sink. Choose socks with reinforced soles made of materials that wick moisture away, to keep your feet dry. Cotton is a bad choice because it retains moisture, so your feet may be wet and prone to blistering. Cargo pants with many pockets and removable legs kill two birds with one stone. Several light shirts are better than one heavy one, as they dry more quickly, provide more warmth through layering and allow you to dress lighter on warmer days. A jacket with a water-repellant or Gore-tex shell keeps wind and rain out and heat in, and is lightweight. Dark clothes are also a good choice, since they'll show stains and dirt less than light ones.
A compact, basic first aid kit, with a first aid manual, is a necessity. You can buy a ready-made one or assemble your own in a strong Ziploc-type bag. It should have stuff for cuts, such as antiseptic solution, band-aids, gauze and tape, as well as Moleskin for blisters. Water purification tablets, if traveling to a developing country, can be a lifesaver if there's no drinkable water around.
