Three small things fix most of what keeps you awake in economy: your head dropping forward, light from the aisle and screens, and engine drone. A Cabeau Evolution S3 neck pillow, a MZOO contoured sleep mask and a pair of Loop Quiet 2 earplugs cover all three and weigh less than a paperback.
Your head: a pillow with chin support
The classic U-shaped pillow has one flaw: your head drops forward the moment you nod off. The Cabeau Evolution S3 is memory foam shaped to support the chin, so your head stays upright. It has a removable cover you can wash, and it comes with a travel case. It doesn't deflate, so expect it to take up space: listings give its weight as between 330 and 370 g. Clip it to your bag instead of packing it.
The light: a contoured mask
Flat masks press on your eyelids and shift when you turn. The MZOO has deep eye cups, so your eyes can open and blink without touching the fabric, and it blocks light from the aisle and from other people's screens. Care is by hand, so wash it in the sink after a long trip.
The noise: reusable earplugs
Loop says the Quiet 2 reduces noise by up to 24 dB on the SNR scale, which is about 14 dB on the NRR scale used in North America. That is a good dent in engine drone and cabin chatter, but it won't silence the plane, and that is the point: you can still hear a flight attendant if you need to. Listen to the safety briefing before you put them in.
Using all three
Put the mask and earplugs in as the cabin lights go down, and keep them in your seat pocket so you can find them in the dark. If you already own noise-cancelling headphones, you may not need the earplugs. See our headphones for flying guide. Pick a window seat for sleeping, and set your watch to your destination's time when you board.