Carry-On vs Checked Bag: What Goes Where

Two different concerns decide where an item belongs. Carry-on rules exist to keep weapons and large liquids out of the cabin, so blades and full-size toiletries get checked. Checked-bag rules exist to prevent fires in the hold, so lithium batteries, power banks, and lighters must stay in the cabin with you.

The two rules that explain almost everything

Once you know which concern applies, most items sort themselves. Knives, tools, and large toiletries get checked. Spare lithium batteries, power banks, e-cigarettes, and lighters stay with you.

Could it be used as a weapon in the cabin, or is it a liquid over 3.4 oz? Then it goes in checked baggage.
Could it catch fire unattended? Then it must travel in the cabin, where a crew member can reach it.

What belongs in your carry-on

Item	Carry-on	Checked
Power bank / portable charger	Required here	Not allowed
Spare lithium batteries	Required here	Not allowed
Vape pen / e-cigarette	Required here	Not allowed
Prescription medication	Recommended	Allowed
Laptop	Recommended	Allowed
Breast milk / formula	Recommended	Allowed

What has to be checked

Item	Carry-on	Checked
Pocket knife	Not allowed	Allowed
Swiss Army knife / multi-tool	Not allowed	Allowed
Full-size shampoo	Not allowed	Allowed
Wrench or pliers 7 inches or longer	Not allowed	Allowed
Wine and spirits	Not allowed	Allowed under 70% ABV
Baseball bat and similar sports gear	Not allowed	Allowed

What is banned from both bags

Fuel canisters, gasoline, and other flammable liquids and gases.
Fireworks, flares, and strike-anywhere matches.
Torch and jet lighters, and lighter fuel refills.
Alcohol over 70% ABV (140 proof).
Marijuana and THC products, which remain illegal under federal law regardless of state rules.
Damaged, swollen, or recalled lithium batteries.

Decide in four questions

Is it a blade, a point, or a club? — If yes, it is a checked-bag item. Wrap it so it cannot injure an inspector or handler.
Is it a liquid, gel, cream, or aerosol over 3.4 oz? — If yes, check it — unless it is medication, breast milk, or formula, which are exempt when declared.
Does it contain or is it a lithium battery? — If yes, it belongs in the cabin. Spare cells are never allowed in the hold.
Is it irreplaceable? — Documents, medication, keys, jewelry, and electronics should stay with you regardless of the rules, because checked bags occasionally go missing.

Gate-checking is the trap

When a full flight forces your carry-on into the hold at the gate, cabin-only items go with it unless you remove them first. Pull out power banks, spare batteries, vapes, medication, and lighters before you hand the bag over.

Frequently Asked Questions

What should never go in a checked bag?

Spare lithium batteries, power banks, e-cigarettes and vapes, lighters, and anything irreplaceable such as medication, documents, or jewelry. Fire risk is the reason for the battery rules.

What must go in a checked bag instead of carry-on?

Knives and bladed tools, tools 7 inches or longer, sporting goods that could be used as clubs, and any liquid over 3.4 oz that is not medically necessary.

Is it cheaper or safer to carry on?

Carrying on avoids bag fees and lost luggage, but it forces you to obey the 3.4 oz liquid limit and give up any blades. Most travelers split the difference: valuables and batteries in the cabin, liquids and tools in the hold.

Do carry-on rules differ by airline?

Size, weight, and quantity allowances are set by the airline; what is permitted through security is set by TSA. An item can clear the checkpoint and still be too large for the overhead bin.