How Much Cash Should I Carry?
In general, it's a good idea to carry between $50-$100, most of which should be composed of small and medium-sized bills (example exchange rates include $20 =10.000 colones, $10=5.000 colones, $4=2.000 colones, $2=1.000 colones.)
Naturally, how much cash you carry with you depends on what you plan on doing. If you are going to the beach for half the day and don't plan on making any big purchases, then $20 should be fine. However, if you're planning on going out for dinner and drinks - and perhaps even making a stop by the local souvenir shop - and you don't want to pay with a credit card, then you should bring at least $30-$50 per person.
In nearly all tourist destinations, if you run out of cash you can always visit an ATM and pull out more money. If you don't want to go to the ATM every other day, keep most of your cash in the safe at your hotel or inside your luggage, then just pull out whatever you need for your daily activities.