The 3-1-1 rule is a rule for liquids through the [[TSA Line]] "Passengers may travel with liquids, gels and aerosols as long as they’re in 3.4-ounce containers in one quart-size resealable bag" They make bags for this specifically, but any *clear* bag that won't be blocked on the scanner should work. If you have [[TSA Line#PreChek|PreChek]] then you can leave it in your carry-on, otherwise, it needs to be taken out and put in the gray bin. --- # References https://www.tsa.gov/travel/frequently-asked-questions/what-3-1-1-liquids-rule