Travel charging is a smaller problem than it looks, once you do the math. The airline limit on a carry-on power bank is 100 watt-hours per pack, and most carriers allow two packs in a single carry-on up to that ceiling. A 20,000 mAh pack at 3.7 V nominal is 74 Wh, which flies without paperwork; a 27,000 mAh pack at 3.7 V is 99.9 Wh, which still flies; a 30,000 mAh pack is 111 Wh and does not. Anything above 100 Wh has to go in checked baggage under most airline rules, which most passengers do not want for a lithium cell. The watt-hour math is the first thing to settle, because it decides the rest of the kit. The second decision is multi-port versus a single high-wattage brick. On a hub-and-spoke itinerary — a long-haul, a layover, a connection — the bottleneck is the seat-back outlet. Two devices on one brick compete for wattage and both charge slowly; two devices on a multi-port PD 3.1 brick each get what they ask for, because the port budget is shared intelligently. A single high-wattage brick wins on absolute peak — a 100 W laptop charge, no compromise — but a multi-port wins on the realistic three-device day: a laptop, a phone, and a pair of earbuds. GaN is the third decision. A GaN wall charger is roughly a third smaller and a quarter lighter than a silicon charger of the same wattage, and it does not run hot to the touch after an hour of full draw. For travel that matters: the brick has to fit in a carry-on pocket without denting anything, and it has to survive being wedged next to a water bottle for a long-haul. The size and weight savings are not rounding errors at 65 W and above. Cables are the fourth item and the most-skipped. A USB-C cable that runs 60 W is not the same cable that runs 100 W, and a cable that runs PD 3.1 at 240 W is not the same cable that runs PPS at 45 W. Match the cable to the protocol — a 100 W PD 3.0 cable with an E-Marker chip for a laptop, a 60 W cable for the phone, a USB-C-to-Lightning cable if any device on the kit is still on Lightning. Skipping this step is why a 100 W laptop "slow charges" at 40 W on the road. Cold-derating is the surprise. A lithium cell that delivers its full rated capacity at 22 °C delivers meaningfully less at 0 °C, and the pack will refuse to push peak output below 5 °C on most BMS units. A ski-trip charger and a beach charger are not the same purchase. For cold-weather travel, look for a published output curve that covers sub-zero, not a marketing line about "all conditions". The travel charging kit, then, is: a power bank at or just below 100 Wh with published UN38.3; a multi-port 100 W PD 3.1 GaN brick (or a single 100 W brick if the laptop is the only high-draw device); one cable per device at the wattage that device actually pulls; and a cold-aware expectation of peak output. That kit covers a flight, a layover, and a road trip without forcing a stop to find an outlet.