Asia and the Pacific: Special care must be taken to insure that your well-meaning gesture is not taken as insulting. If you are unsure, it is best not to tip. If possible, observe the locals and follow their lead.
Europe: Many hotels and restaurants add a service charge to the bill. In most cases, an additional tip is unnecessary. If no service charge is added to your bill 10% is the general rule for restaurant service, a dollar per bag will be appreciated.
Middle East/Africa: While your tip will not be seen as insulting, it may be unnecessary. Once again, the best bet is to do as the locals do.
Central/South America: Many hotels and restaurants add a service charge to the bill, and an additional tip is unnecessary. If not, 10% is the general rule for restaurant service, and a dollar per bag is appreciated.
The Magellan's tipping guide is just that, only a guide, and they indicate the practice is a reward for good service and in the end the value it up to you. Below are some popular destinations and tipping guidelines.
Restaurants: 10% in fine restaurants only
Porters: $2 per bag
Taxis: Round Up
Porters: $1-$2 per bag
Restaurants: 10% if no service charge
Porters: $1 per bag
Restaurants: None, tipping is perceived as insulting
Visit magellans.com for the complete list which features guidelines for over 70 countries.