The ultimate packing list

2 pairs of pants (men/women)—Take quick-dry travel slacks (with secret pockets); I always make one a pair convertible pants so I don't need to bring extra shorts.
1 pair of shorts or convertible pants with pockets (men/women)—European adults don’t often wear shorts, but they’re good for hiking and, for men, as swimsuits (women: buy a swimsuit there if you need it).
1 long skirt or dress—The skimpiness at which your respectability will be questioned varies with the country, so hedge your bets with something long.
4 pairs of underwear (men/women)—They even make disposable underwear now for men and women.
4 bras or camisoles
4 pairs of socks
3 T-Shirts/tanks (men/women)—Wear under long sleeves so the easily washed T-shirt will soak up all the sweat. Get quick-drying tops, not cotton.

2 long-sleeve shirts (men/women)—Button-down collared shirts are respectible enough for all occasions, and travel ones have hidden pockets, sun block, and easy washability built in.
Sweater (men/women) or blazer (men/women)—Warm, and dressy. I go for the sports jacket (for pockets), though in winter also bring a thin sweater for layering.
Jacket (men/women)—Only necessary fall through early spring.
Long Underwear (men/women)—Only for visiting northern countries from late fall to spring.
Good walking shoes (men/women)—No dress shoes, heels, flip-flops, or anything you can’t walk in all day for two weeks straight. (Travel-worthy Mary Janes are also OK.)
Hat —The Tilley Hat is the ultimate travel topper.
Belt—Those with a hidden zipper let you hide your passport photocopy and some emergency cash.

Toothbrush & small tube of toothpaste
Small soap bars & small shampoo—Bring the soap sliver from your bathtub to start; steal more from hotels as you go.
Razor & shaving cream—(Battery-op shavers are O.K. (electric razors just bring the hassle of electrical converters and adaptors).
Medicines—Prescriptions should be written in generic, chemical form (not brand name).
Extra glasses and contacts— Count on losing them, and bring a hard glasses case. Also, bring enough saline solution to last (parts of Europe sell it only in glass bottles).
First-aid kit—Take at least: a few Band-Aids, antiseptic ointment, moleskin for blisters, aspirin, Dramamine or motion-sickness wristbands, hand lotion and lip balm (traveling promotes chapping), sunscreen, Pepto-Bismol (indigestion and diarrhea), and decongestant.
Comb/flat brush

Laundry kit—To do your wash on the go in the bathroom sink, you need travel detergent (biodegradable), a braided clothesline (the twists act as clothespins), a sink stopper, and I suggest the truly remarkable Stain Eraser and Janie Spot Cleaner (perhaps I'm a slob, but I need them at least once per trip). All available at travel and camping stores, or from Magellan's.
Towel—H2G2 fans don't need to be told this, but a shammy-style camping towel or even small terrycloth towel is a lifesaver when confronted with Europe’s nonabsorbant, waffle-pressed jobbers.
Feminine hygiene products—You can buy tampons abroad, but take what you need with you, especially if you’re brand-loyal.
Condoms—US brands are safer.
Pocket-sized tissue packs—Invaluable for sudden spills, substitute napkins, bathroom emergencies, signaling surrender, and, if still clean enough, runny noses.

Guidebooks and phrase books
Journal and pens—You won’t remember it all half as well as you imagine.
Camera— Bring extra batteries. Tote it in a purse or mild-mannered daypack, not a “steal-me” professional camera bag.
Film/Memory Chips—Very expensive in Europe. Airport X-rays will fog higher speed films, so stow the rolls in large, see-through plastic baggies for hand-inspection.
Tripod—I like QuikPod set that includes both a miniature tripod and a telescoping monopod designed to extend your reach to take pictures of yourself (YouTube here you come!).
Tiny flashlight
Travel alarm clock—Battery powered.
Plug adaptors—For charging your digital camera, cell phone, etc.
Chargers/cables—I carry all my plugs, cables, and adaptors in a small toiletry bag.
Cell phone —Only bother bringing yours if a tri– or quad-band world phone with AT&T or T-Mobile (on the GSM standard used in most of the world).
Sunscreen
Bug spray—Most countries have yet to discover window screens.
Swiss Army Knife or Leatherman/multitool—Most useful features: screwdriver/can opener, blade, corkscrew (for picnics), tweezers, scissors, nail file. Remember: pack it in your checked luggage.

Address list—Friends appreciate postcards at the time more than a slide show afterward.
Small bottle of water—Buy them as you go, but always have one; outside of Europe and the North America, carry a bottle with a built-in purifier or get a sterilizer.
Luggage locks—Get enough for every zipper; make sure they're the kind approved for TSA use.
Sleep Sack—If you'll be camping or staying in hostels.
Tiny folding umbrella
Sunglasses
Pocket sewing kit—Trust me.
Duct tape—Ditto.
Novel—For long plane and train trips. Many hotels have rotating bookshelves to trade for a new one when you’re done.
Teensy binoculars—Maybe I'm getting old, but increasingly I find these useful for admiring distant frescoes, wildlife, landscapes, popes, etc.
Driver’s license & International Driver’s Permit—Only if you plan to rent a car.
Wallet—But keep important stuff it the moneybelt.
Money—Credit cards, ATM bankcard, traveler’s checks, and cash (euros if you got 'em and some emergency dollars).
Passport—You won't get very far without it.
Airline tickets—Crucial.