I try to travel going carry-on only; and for me, the following are mandatory in-flight items:
(i) microfiber fleece blanket stored in a silky shoe bag with a cinch drawstring (I’ll admit I pinched this from a flight many years ago … but at least I know it is clean!), (ii) TRTL neck support, (iii) Bose NC headphones, (iv) Dream Essentials eye mask, and (v) EconoHigh Portable Footrest (since I’m 5’3” this makes coach seating more comfortable).
In flight, I wear a fleece jacket (even in summer). I also have an “airplane kit” containing: a pkg of disinfecting wipes, a couple of pieces of hard candy, gum (enough for each take off & landing), an emery board, a ballpoint pen, and a handheld Japanese folding fan (ever been on a plane with no air? ... ugh!).
All of the above items are packed into a RS Veloce knapsack (not expanded) along with my Kindle, iPad, and 311 TSA liquids bag. Since the knapsack is not expanded, there is ample room for sandwiches, snacks, and water bottle.
After every trip I've taken (~17 … all in coach), I’ve tried to evaluate what worked well and what didn’t. I’ve found the above items indispensable. Before de-planing, I make sure to disinfect the footrest with wipes before packing back into the knapsack.
Lastly, I wouldn’t suggest using a mylar emergency blanket on a plane … while it may be effective at keeping you warm, the crinkling noise made with every movement will likely make your fellow passengers less than happy. And the Ikea fleece blanket, a good and inexpensive ($4) suggestion, simply weighs too much at 1 lb., 4 oz.