Don't carry a credit card? Under 25 years old? Renting a car just got a whole lot easier. Two budget-minded rental car companies, Thrifty and Dollar, now accept debit cards with virtually the same ease as credit cards. And here's the kicker: The minimum age to rent a car with a debit card is just 20 years old.

Flying into a city and need to get downtown? Or staying in a city and need to get to the airport? Consider ditching the taxi or Uber and renting a car instead. Three major rental car firms—Avis, Budget and Alamo—offer a 12-hour one-way airport-to-downtown rental in participating cities starting at $9.99.

Planning on renting a car in Ireland? Be careful. Multiple recent news stories indicate that the island synonymous with hospitality has also developed a nasty reputation for ripping off rental car customers. Here's how to avoid getting stung.

Did you rent a car from Dollar or Thrifty in Florida anytime in the past eight years? If so, you could have some money coming to you.

What's in your wallet? If you have a Costco membership card, it may be the ticket to a fantastic rate on your next car rental. Costco has partnerships with four major rental car companies: Avis, Alamo, Budget and Enterprise.