Each place you visit has things to do. "Adventure" activities - speed boat trips, parasailing - museums, parks, national parks, theme parks, attractions.
Before you travel, you should work out what you might like to do, and budget for those. Some things are free too - like wandering in a park or laying on a beach.
Don't forget food. Will you be able to cook your own food? Will you buy all your food? Where? Restaurants or take-away places?
Estimate - Activities (each activity)
Amount to budget?
Multiply the activities cost by the number of activities you want to do.
Multiply the meals each day by the number of days.
Add the two, then add a few dollars for unexpected costs.