Most airlines allow passengers to have one carry-on bag and one personal item. But many people need something else-- layers or a blanket to keep them warm.
Airplanes are notoriously chilly, but it turns out there’s a medical reason why the cabin temperature is kept so low.
A study from the American Society for Testing and Materials looked into the correlation of in-flight fainting and cabin pressure and temperature. Due to a medical condition called hypoxia, people are more likely to faint in the air than on the ground. Hypoxia occurs when body tissue does not receive enough oxygen. High cabin pressure can also exacerbate this condition.
Basically, if the cabin temperature is too warm, it can cause someone to faint. And since everyone’s body temperatures are slightly different, airlines err on the side of safety and keep the temperature extra low. http://www.rd.com/advice/travel/why-is-it-so-cold-on-airplanes/
According to retired Delta pilot Paul Eschenfelder, newer airplanes have more advanced thermostat systems and can regulate temperatures in individual rows - so you might have a more enjoyable experience on those aircraft.
In the meantime, your safest bet is to bundle up.