Great question — answering as the UphillTech team:
Or, is carrying an extra backpack, apart from that 7kg carry-on luggage, is banned? In theory, yes it is banned. From Etihad's baggage calculator (check your itinerary there to see whether you get the same info): In practice, some airlines don't check it often (that partly depends on how big/heavy your bags look). And given a specific airline, the way they check may depend on the airport (e.g. Air Asia in KTI vs. Air Asia in KUL T2).
Full answer by Franck Dernoncourt: https://travel.stackexchange.com/a/204563 (CC BY-SA 4.0).
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