Leaving Your Money in Easy-to-Pick Places
This is the only mistake on this list that I didn't personally commit, but it did happen to my mom in Rome. Her husband paid for train tickets in cash, then returned the envelope to his backpack. A seasoned pickpocket spotted the envelope and swiped nearly $500 in Euro without either person noticing. Keep your money in an exceptionally secure place to avoid this happening to you. There are even clever travel accessories that can help.