McDonald's ketchup or Taco Bell hot sauce can be used to clean dirty pennies.

I know what you're saying..."the hot sauce seems reasonable...but ketchup? Really??" And yes, I probably would have agreed with you before doing this research. But it's true - both ketchup and hot sauce can be used to polish up your copper cents! These condiments do not necessarily need to be from McDonald's or Taco Bell, however. In fact, they don't even need to contain tomatoes or spices! The secret to the cleansing power of these flavorings is actually far simpler than you'd think. All you need is some vinegar and common table salt! The combination of salt and vinegar allows the copper oxide on a penny to be broken down and converted into copper chloride, or in simpler terms, the penny gets cleaned.

For all you science whizzes who'd like to know the chemistry behind this sort of reaction, read more here.