Remember to pack things that are essential for the trip such as documents (passport, plane tickets, driver's license, credit cards and foreign currency, if traveling to a foreign destination); toiletries in small containers properly sealed in zip plastic bags; medications in original containers and photocopies of prescriptions; and walking shoes for the adventurous type. Also carry some extra plastic bags, as they may come in handy to pack various things during the trip.
Depending on the duration of the trip, pack pants, a few shirts, underwear and socks. For cold weather, carry a fleece jacket or a sweater, as it is lighter. Also it helps to carry thermal underclothes for both the upper and lower parts of the body, so you can save space, instead of carrying heavy warm clothes. For warm weather, consider taking clothes in cotton/polyester blends, because they are light and dry easily. Consider doing your own laundry every day so that you can manage with minimum clothing in your luggage.
Have some nutritional snacks and a bottle of water handy when packing for a trip. This becomes essential if you are traveling someplace where the quality of food available is questionable. Or it could help to ease hunger pangs during long waiting periods. Carry a "Steripen" to sterilize the water at places where you think the water is not safe to drink. It helps to get pure drinking water without waiting for the restaurants to do it for you.
If you are carrying a camera, pack a few extra rolls of film. For a digital camera, remember to carry the camera charger. A torch or LED light will be useful for any trip. Take a few extra AA batteries along with you. If traveling abroad, be sure to carry phone and power plug adapters as well as a voltage adapter for both low- and high-voltage devices.
