How to avoid extra fees when traveling?

Although charging for checked luggage has become quite commonplace, not all airlines charge extra for your first suitcase. Weighing your suitcase before arriving at the airport can help you avoid surcharges for overweight luggage.
Booking your airline ticket in advance can result in lower ticket prices, and you’ll have a better selection of seats. Try to have travel plans solidified before booking, though, since ticket changes can result in additional fees.

International banking fees can accumulate if you’re traveling outside the country. Foreign banks and ATMs sometimes charge extra for banking with their institutions. Some online banking platforms don’t charge more for out-of-network ATMs, though.
In some cases, credit cards that offer travel rewards will not charge extra fees for international use. Alerting your bank of international travel plans can reduce the chances that your account will be frozen for perceived suspicious activity.

Cell Phones.
Cell phone companies can assess extra roaming fees for usage while traveling. Some cell phone companies have online travel planner services that allow you to estimate how much data or texts might cost while traveling.
Using wireless Internet when it is available can help lower your cell phone bill while traveling. It’s possible to rent a wi-fi “bubble” that can create online access while traveling to reduce roaming.
Some cell phone companies also offer special international travel data packages to help avoid additional fees on your typical plan.

Rental Cars.
Rental car contracts can be confusing, creating opportunities for hidden fees and surcharges. Your standard auto insurance coverage might cover car rentals, making additional coverage unnecessary.
Sticking with one driver can eliminate extra fees for additional drivers behind the wheel. If you’re not driving the rental car while traveling, leave the key in your hotel room in case you’re pick-pocketed.
Replacing lost keys can be costly. Choose the option to refuel your own vehicle rather than paying per-gallon for the car rental company refill; the latter is usually more expensive.

Based on eHow article.