A short list of gadgets that earn their space in a carry-on, a second list of ones that often do not, and five questions for deciding about anything else.
Packing lists tend to grow because each gadget solves a small problem, and the sum of small problems is a heavy bag. A better test than "might it be handy?" is whether the item removes a task you will certainly face on this particular trip, and whether it can travel and run where you are going. Below are two buckets, followed by the rules that sort anything else.
The USB Implementers Forum describes USB Power Delivery as a system in which devices negotiate the power they need; earlier versions topped out at 100 W, and revision 3.1 allows up to 240 W over a suitable cable. For a traveller the point is simpler: one wall charger can serve a phone, earbuds and, often, a laptop. Check the laptop's own power supply label for the wattage it expects, and note that the cable has to be rated for the power as well as the charger.
For long travel days a power bank is the most useful single item, but it is also the most regulated. See the battery rules below, and Portable Chargers: Understanding Capacity and Charging Speed for how capacity and speed work.
An adapter fits the socket and does nothing else. Energy Safe Victoria advises looking for the RCM mark and insulated plug pins, and Electrical Safety First says UK-sold adapters must meet BS 8546 and that some suit only double-insulated devices. Whether a device can run on the local supply at all is a separate check, explained in Travel Adapters vs Voltage Converters: What Each One Actually Does.
Short cables take up little room and tangle less. A pair covers a phone and a second device; a third is rarely needed if the charger has several ports.
Not a gadget, but the habit that saves the most trouble. Charger, cables, adapter and power bank live together in one pouch that goes in the cabin bag. It means the battery-bearing items are already where the rules want them, and that the charger left plugged in beside a hotel bed is the first thing you notice missing at checkout. It also makes a security-line check quicker if a bag is opened, since everything electrical is in one place.
This list is a judgement, not a rule. A photographer may reasonably carry a chunky charger; a long-haul cyclist may want a bigger power bank. The point is that each item should be there on purpose.
Transport Canada's 2025 safety alert says spare lithium batteries, including power banks, must be carried in carry-on baggage only, that terminals must be protected from short circuit, and that if a carry-on is checked at the gate, spare batteries must be taken out and kept with you in the cabin. The UK Civil Aviation Authority says to always take power banks into the cabin and never charge one on any flight. For batteries rated above 100 Wh and up to 160 Wh, CATSA says spares need air carrier approval and are limited to two per person in carry-on. Airlines may set tighter limits of their own, including on how many power banks you may carry, so read your carrier's page before you pack.
Capacity is printed on many power banks in mAh, but the rules use watt-hours. Watt-hours equal volts multiplied by amp-hours. Battery University gives lithium-ion cells a nominal 3.6 to 3.7 V, so a 20,000 mAh bank works out at about 74 Wh (20 Ah × 3.7 V), under 100 Wh, while a 30,000 mAh bank is about 111 Wh (30 Ah × 3.7 V), in the band needing approval. These are illustrative arithmetic; always use the Wh figure printed on the product where there is one.
A "no" on the second or third question usually ends the discussion. A "no" on the fourth is the quiet reason most drawers of gadgets exist. Anything that comes through all five is probably earning its place, and the answers can change with the trip: a week of city hotels asks different questions from a fortnight of camping, where a larger battery may be sensible if you drive there rather than fly; and if you want to keep track of the bag itself, Bluetooth Trackers: What They Can and Cannot Do explains what trackers can and cannot do.
Before you zip the bag
How we research. Based on manufacturer documentation and the sources listed below. Know Your Gadget did not test products for this article. See our editorial policy.
Everyday Tech
The biggest number on a power bank, its mAh rating, is the hardest to compare. Watt-hours, conversion losses and USB power negotiation explain what you really get, and what airlines look at.
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Outdoor & Travel
An adapter changes the shape of a plug. A converter changes the voltage. Mixing them up is the most common way to damage a hair dryer on holiday.