Get a powerbank, preferably at least 10000mAh and pick the most lightweight one; there are many with similar pricing for surprising different weights.
Going cold places? invest in fleece jackets; they are lightweight, keep you warm, dry fast and can also be found other than polyester if you’re sensitive to it. Having a sporty neck scarf and a set of fingerless gloves is a smart way of reducing heat loss.
Another smart choice is to buy a fleece towel; similarly it dries quickly, it’s very lightweight and takes little space.
Can’t sleep on the airplane? definitely get an eye mask. Also a noise cancelling headset could dramatically improve the flight experience! otherwise a pair of ear plugs would help too.