Before heading to Incheon Airport, separate items that can trigger security delays so you do not have to repack at the checkpoint.
For international departures, Incheon Airport says liquids, sprays and gels in carry-on baggage must be in containers of 100 ml or less and placed in one transparent 1 L zip bag per person. The rule applies to products such as drinks, lotion, toothpaste, shampoo, gochujang and kimchi when they are liquid or gel-like. Duty-free liquids are handled separately when sealed in the approved duty-free liquid bag.
For batteries, spare power banks cannot go in checked baggage. The airport's current guidance allows spare lithium batteries under 160 Wh in carry-on, with airline approval required for 100–160 Wh units and a limit of two in that range; batteries over 160 Wh are not allowed. Airline rules can be stricter, so check your carrier as well.
Liquid medicine above 100 ml may be carried when necessary for the flight if you have a doctor's note or prescription in Korean or English and the security officer accepts it. The airport recommends checking airline requirements too.
Do a final check the day before departure because airline, destination and transfer-airport rules may differ from Incheon Airport's baseline guidance.