I was reading this article and came across the term 'cooler bag'.
Looking up on the web, they seem to be Thermal bags in which you can have food items. Now if I were to bring food in such Thermal bags, would they be counted as part of carry-on allowance or not ?
I ask as food is something I would eat either in the airport or in air if no meals are being given etc. so it would not remain static as other things, clothes, laptop etc.
This is very complicated. Sure, a thermal bag is a bag, end of story, but what do you plan to put inside it and where?
In general, carrying cooked food across security is near impossible where liquid restrictions are in effect. You'd need to have some food which does not have any liquid and even then they might deny you because pasta, certain kind of sausages, cheese spread etc count as liquids.
It becomes more interesting if you buy food at the airport past security because some airports will allow you to buy food you can carry on and if you move a cooler bag from your carry on to the inside of the "food on the fly" paper bag just so the food lasts longer, I do not see it causing a problem.
It's not part of standard allowance.
Standard definition of carry-on or hand luggage (example from Lufthansa) is "1 piece", I've never seen an exception for additional food bag. Unless, like in Ryanair, you're just allowed to carry two pieces, but then it doesn't matter if it's food or not.
About consuming it during the flight - hand luggage allowance is (usually) checked when entering the airplane, so the fact that you will eat it during the flight doesn't matter. Your one piece of luggage should fit in overhead compartment / under the seat during the whole flight.
