Passengers on planes always have a constant battle over the temperature that they
think the plane should be at and stewardesses and the cabin crew will have to accept that every request is valid and continue to adjust the temperature of flights to respects their customers' wishes. For people who are to polite too speak up, it can sometimes cause the cabin to become much to cold.
Unlike a warm cabin which in all likelihood will just make you fall asleep, a cold cabin can be very uncomfortable and make the whole experience of your flight a very un-enjoyable one that ends up making you unhappy you travelled in the first place. Again, you can ask the cabin crew to change the temperature to warm up the plane a little but often they will want to keep it at a constant temperature that they have learned is a very happy medium that will make all the customers on the plane as happy as is possible.
To prepare for the eventuality of a cold plane you should always remember to bring a warm sweater. Wearing a coat that you bring on the will likely be too uncomfortable, especially if it is too bulky to be the sort of coat that you can sit in for hours on flights from Portland to Boston or flights from San Francisco to Denver. So bring something that is both light and comfortable light a pillow, but something that will be able to warm you up even when you're in the coldest cabin. With a nice big comfortable sweater you won't need to worry about the battle over the temperature of the cabin and you can just relax and enjoy your flight.