It is the most common thing is to just pull your wallet out whenever you need to pay for something. But in a foreign country where pickpockets might be watching you this is not a good idea, because you are letting them know where you keep you money making their job easier.
Read more tips for traveling to Central America.
My advice is to sneak away to a washroom or some other place away from prying eyes to take out just enough money for your current needs. Another way to avoid being robed is to keep your wallet in some place where it’s not visible. Don’t carry your wallet in a back pocket. It is really easy for a thief to get it out from there. Remember they are professionals!