Mad Money, Pocket Money, Walk Around Money or Street Money.  Whatever you call it, how much is the right amount?

Used to be that cash was king and people literally carried some cash on them at all times.   Now days you can be hard pressed to find cash on anybody with the prevalence of debit and credit reading devices.
But the best prepared  among us know that cash always plays and can always pay  so just how much cash should an adult carry on them at any given time these days?
Yahoo reports that a survey from Money magazine found 42 percent of people carry no more than $40 in cash. Another 30 percent carry between $41 and $99.  Ok, but is that enough if you really need it?
Popular opinion collected  from a variety of sources says carrying $200 is just the right amount because it is enough to handle a standard emergency, and it's likely enough to cover a bill at a restaurant if the restaurant doesn't accept plastic or worse yet - your credit card gets declined.
Perhaps in the past you've seen the ads for travel guides saying something like "See Europe on 50 dollars a day."?  Well it costs a little more today to see the USA !   BudgetYourTrip.com says it costs an average of $221 per person for each day traveling within the U.S. And the experts also say you should have at least $20 in five dollar bills on you at all times, for tipping.