Every time you fly domestically in the U.S., a similar scene unfolds in front of the TSA checkpoint.

People stand in line with their bags, constantly wondering to themselves, "Can I bring this?" 

Here's a calm breakdown of the items that are particularly confusing.

The most commonly confused item is water. The rule is clear: you cannot bring in water that is already filled. Whether it's a 500ml bottle or a small water bottle, it must be discarded at the checkpoint. However, empty water bottles are fine. You can pass through with an empty tumbler or plastic bottle and refill it at a water fountain inside. Therefore, frequent travelers often just bring an empty bottle, which is the simplest method.

Lunch boxes or sandwiches can generally be brought in without any issues. Solid foods like kimbap, sandwiches, salads, bread, snacks, and nuts that you packed from home have very few restrictions. However, be cautious with liquids or runny foods. Items like seaweed soup, porridge, soup, yogurt, and pudding are likely to be considered liquids. So, it's best to prepare solid foods for your travel meals to avoid any hassle.

Baby food is handled a bit more flexibly than adult food. Small pouches or jars of baby food are generally allowed. However, they may undergo additional screening during the process. They might open your bag for inspection or use special equipment to check it. While this can be a hassle for parents, it falls within the allowed regulations, so there's no need to worry. Just make sure to allow a little extra time.

Pre-made baby formula is a different situation. The general liquid rule is a 100ml limit, but exceptions apply for baby formula or breast milk. You can bring as much as you need. However, this may also be subject to additional screening. In some cases, you may be asked to taste it yourself. If this situation is uncomfortable, you can just pack powdered formula and mix it with water at the airport, which many parents choose to do.

Fruits like bananas and apples can usually be brought without any issues. Whole fruits have fewer hygiene concerns and are not considered liquids, so they are not regulated. A few bananas, one or two apples, or a tangerine typically pass through without any comments. However, it's considerate to be mindful of strong-smelling fruits when eating them on the plane.

Lighters are generally allowed on board. A small standard lighter in your pocket is usually permitted. However, having multiple lighters in your checked luggage or using types that leak fuel can be problematic. Especially, torch-style lighters are often denied entry.

The size of knives is crucial. Small folding knives or paring knives are not allowed in the cabin and must be checked. Long kitchen knives are, of course, not permitted in the cabin either. If you need one during your trip, it's best to buy it at your destination.

Guns cannot be brought into the cabin under any circumstances. Even legal firearms must be declared and placed in a special case to be checked. The process is complicated and time-consuming, so it's best to arrive at the airport early.

Gas is generally considered a hazardous material, making it almost impossible to bring on board or in checked luggage. Camping butane or propane canisters cannot be taken. It's best to purchase them at your destination.

Batteries vary by type. Lithium-ion batteries for phones, laptops, and cameras can be brought on board, but checked luggage may be prohibited. Power banks must also be carried in your bag. Large industrial batteries are mostly restricted from being brought on board.

By keeping this information in mind, you can reduce the confusion the next time you fly. Ultimately, the regulations are not meant to inconvenience us but to ensure everyone's safety.