Shop around or barter for a better deal
Americans are accustomed to fixed prices; citizens in other nations are more accustomed to haggling over goods and services. Make a counter-offer before you agree to buy that memento or sign up for that trip. You might be able to negotiate a lower price with a dealer.
Likewise, don’t choose the first restaurant, shop, or tour company you come across. Take a look around. The $10 T-shirt at the first store could cost $7 in the second. The price of a burrito lunch may drop by a dollar or two as you travel away from the main tourist area.
Before you sign up for that snorkeling trip or city tour, get prices from a few different tour providers. It may not always work, but when you find the best-priced option, your comparison searching will pay off.