What are good items to pack for a deployment?

A good headlamp and crocs. Crocs are years ahead of anything else for shower shoes.

A hard drive with 9 months worth of movies and shows. Or other stuff to keep you comfortable and entertained.

Crocs, 2 woobies for your bunk privacy, and at least $200 cash so you can get a puck or sim card depending on your phone. If you barely use it at home you’ll never use it over there so don’t take extra stuff. You can literally get anything over there so pack light (you will take a long walk with all your bags). Mentally and physically prepare to be there longer than what they tell you. My 9 months turned into 16 months last minute. Good luck.

Despite what you have heard. It gets cold. Bring some hoodies.
Crocs are not only a shower shoe. But wall fighting footwear. And lounging around kicks.
Hard drive with movies. I can not stress this enough.
Baby wipes. All the baby wipes.

A computer, do school there. Trust me, you will have internet.

My Nintendo switch came in handy once covid became a thing. Seems like everyone else already hit the real good stuff...crocs, hygiene/baby wipes, hoodies, laptop/hard drive...you’ll be G2G.

Crocs, headphones, portable chargers, box cutter, power converter with the outlet adapters for different countries, external hard drive, laptop

Your command should issue a packing list. I never liked headlamps makes a great target, just the good old fashioned army flashlights with a red lens. Always have a knife of course, nothing too conspicuous for most places, but it all depends on your MOS, your unit, section or unit. Got to have a gerber but I got one with each deployment I went on from the unit. Bring a deck of cards and learn to play spades if you don't already know.

Something I haven't seen mentioned are power cord adapters. Chances are you're going to be bringing some electronics from home. You'll need adapters to plug them in. A 110 power converter is also probably a good idea, although you may be able to buy one when you arrive.

I will agree with what many have already listed: headlamp, crocs, hard-drive (with movies/TV shows), etc.
My personal preferred items are an extension cord (8'-12') and fitted and flat sheets. An extension cord because you never know how far from the outlet your bed will be. I think personal sheets are under-rated. Having a fitted sheet beats having to do the whole hospital corners thing, since billeting will sometimes only issue a flat sheets. The extra flat sheet is great if the room is too hot and also, I think, feels more comfortable if you are required to use your sleeping bag.