If solo here are my tips. An overnighr flight i get onboard in normal clothes. Have dinner etc watch a film. Then few hours in to flight change into comfy bottoms and top and take off bra. Fluffy socks. Brush teeth and treat it a bit like bed time and relax/dose. daytime just make sure youre comfy and slipper socks.
Noise cancelling headphones are your friend. I invested in some bose ones. Best thing i ever bought. I sleep with them on a plane. Block out crying babies, random chitchat etc.
Snacks. Airplane food is a bit meh at times and also never served when you get peckish.
Tablet filled with your favourite series to binge.
Take your own pillow (even a small cushion is better than airplane ones).
A big snuggly hoody and i find a big pashmina type scarf. Helps keep you warm and snuggly in flight when sleeping.
Water. Buy a big bottle at airport and take on board.
Also make sure you have medication basics on you in case of air presure headaches or whatever.
Finally toothbursh, deodrant and fresh underwear for when you're about an hour ish before landing. Go freshen up. Put bra back on if you took it off. Feel 'awake' again even if you've had next to no sleep.