For many, one of the most disconcerting aspects of traveling, especially when traveling abroad, is the tip. Who do you tip? When do you tip? How much do you tip? Is tip included? Do I have to tip? Are there times when I shouldn't tip? Are there places that don't allow tips? The list goes on and on...and continues to cause those uncomfortable moments outside the courtesy shuttle as you dig through your pockets for ones.

Allow me to help. Here are some "tips" (har har) from "Emily Post's Etiquette" (16th edition) and Tipping.org. Whether you travel once a decade or every other day, we all can use a reminder as to who gets a tip, who doesn't get a tip, and how much they're expecting.

Airport workers:
-Skycaps: Usually get $1 per bag.
-Wheelchair attendants: $2-$5.

Cabbies: 15 percent of fare.

Coat check: $1 per item.

Cruise ships: Check with the specific cruise line, as many of them have their own gratuity guidelines.
-Cabin stewards, wait staff: $3 per day per person, according to the Cruise Lines International Association, an industry group.
-Busboys: $1.50 per day, per CLIA.

Hotels:
-Bellhops: $1 per bag.
-Concierges: Anywhere between $2 and $10, depending on the service provided (i.e., dinner reservations, show tickets).
-Courtesy shuttle drivers: The Las Vegas Chamber of Commerce suggests at least $1 or more per person, or $4-$5 per party.
-Door attendants: $1-$2 per bag, and $1-$3 for calling a cab.
-Housekeepers: $1-$2 per night, left in a sealed marked envelope.
-Room service: 15 percent of bill, unless gratuity already is part of the bill.

Limo drivers: 20 percent of the bill.

Restaurants:
-Buffet-style wait staff: Five to 10 percent of the total bill, depending on exactly how much work the wait staff actually does. However, the Las Vegas Chamber of Commerce says the standard tip in that city -- renowned for its cheap and plentiful buffets -- is $1 per person served "if a server is helpful and gets your drinks."
-Wait staff: 15 percent to 20 percent of the total bill -- closer to the latter if the service is particularly good. Exception: If a wine steward, or sommelier, picks and serves the wine (see below), the wait staff's tip should be 15 to 20 percent of the food bill only (emphasis mine). Watch out: Some restaurants add a gratuity of 15 percent or more to a tab for large parties; look before adding a tip.
-Bartenders: Ten to 15 percent of the bar tab.
-Wine stewards, or sommeliers: Fifteen to 20 percent of the wine bill.

Tour Guides and drivers: For extended tours, $1-$2 per person per day; for day trips, $10 or 15 percent of the tour cost per person.

Train personnel: Amtrak spokesman Kevin Johnson stresses that "tipping is not a requirement" on Amtrak trains. However, he did disclose a few "rules of thumb" on trains:
-Dining car waiters, stewards and bar car waiters: 15 percent of bill
-Red caps, or porters: $1 per bag
-Sleeping car attendant: $5 per passenger per day

Valet parking: $1, handed off when the car is returned.

International tipping customs

If you're heading overseas, check the tipping customs. Some cultures have adopted some U.S. tipping customs; others may consider tipping offensive.

Windham International , a company that specializes in helping U.S. expatriates relocate overseas, offers information on international tipping customs.

Beijing: Not customary.

Dublin: Largely not expected; service charges usually are included in the bill. Cab drivers are tipped 10 percent; bellhops and porters are usually given 1 Irish punt per bag.

Istanbul: Depends. Cab drivers don't expect it, but rounding up 10,000-20,000 lira is much appreciated. A 10-15 percent service charge is included at everything but the cheapest Istanbul restaurants, but that fee rarely is given to the waiter. Current custom dictates that an extra 10-15 percent be left on the table or handed to the waiter. Staff at a Turkish bath usually expects a 30 percent tip, which is shared.

London: At restaurants, 10-15 percent if not included on the bill. For cabs, 10-15 percent.

Manila: At restaurants, 15 percent. For cabs, 5 pesos.

Mexico City: At restaurants and for cabs, 10-15 percent if deserved.

Paris: Restaurants usually include gratuity on the tab; look for the term "service compris" on the bill. However, leaving a little extra is customary for good service. For cabs, 10 percent.

Prague: At least 10 percent for restaurants and cabs.

Rome: At restaurants, a 15 percent service charge usually is added to bills, but it doesn't all go to the waiter; leaving an extra 5 percent is customary.

Singapore: Not customary; in fact, Singaporeans become upset when they see tourists tipping. The one exception is hotel bellhops, who are usually tipped 1 Singaporean dollar per bag.

Sydney: According to the tourism site DiscoverSydney.com.au, tipping is not expected. However, a small tip (10 percent) in a restaurant is "appreciated" if the service is exceptional. Bellhops usually get a few dollars; however, some hotels discourage tipping.

Tokyo: Not customary.

Toronto: At restaurants and for cabs, 15 percent.