In 2026, the 3-1-1 rule remains the global standard for carry-on luggage: all liquids, gels, and aerosols must be in containers of 3.4 ounces (100ml) or less. These containers must fit into a single, clear, quart-sized (one-liter) plastic bag. "Liquids" include things many people forget, like toothpaste, mascara, lip gloss, and even creamy cheeses or peanut butter. A supportive 2026 update: many airports now use advanced CT Scanners that allow you to leave your liquids inside your bag, but the volume limits still apply. Exceptions are made for medically necessary liquids (like insulin) and baby formula/breast milk, which should be declared to the agent. To save space, I highly recommend switching to solid toiletries like shampoo bars, solid cologne, and toothpaste tablets, which do not count toward your liquid limit at all and are much more environmentally friendly.