What piece of gear would you tell a first time deployer to make sure to have?

After retirement from the AF I worked in the BX. When troops were deployed after 9/11, anything to reduce chafing in the tender areas! Camel back water carriers were also popular. Many troops were looking for a better quality boot but those were not normally on our approved list and any boot not of US manufacture was not approved for wear as by act of Congress.

Laptop and ear buds. Great for Skype, email, movies, and music. You might be in the middle of BFastan and a network will be available.

A case of TANG, orange, strawberry or grape. The taste of bland water overseas will be a damned sight better with some flavor and sugar.

Really depends on how established the theater of ops is. 2005 we still didnt really have internet, so it was all portable dvd players and books.
2010 we had unlimited internet in our room for $75 a month so a decent computer was more than enough. 2019 was a computer and all books for grad school. So theres a lot that goes into it

The one thing I wish I had known before hand and had taken with me would've been the huge ziplock bags to keep my clothing in. Always seemed to be coated in the fine sand dust of the desert

My wife went to Desert Shield / Desert Storm with her medical unit out of California. I was the First Lieutenant on an LST training Marines off San Diego. We communicated a lot by phone messages. The first one I got from the UAE was a plea for about two footlockers of 'sanitary supplies'. Seems most of the women were in dire straits and the Army was clueless. I copied down the list and headed for the grocery store, even though I'd never heard of most of the gear. I parked my cart in the hygiene aisle and was staring hopelessly around when a woman came up wondering if I was some kind of perv. As I told her the story, two other women had stopped to listen. When I was done, the woman grabbed the list out of my hand and the three of them started throwing mysterious packages into my cart. When they were done, I mumbled my thanks and headed for the checkout. I did remember to ask for a couple of large empty boxes. At home I packed, wrapped, taped and addressed. Cut to the chase....the goods got to the ladies in short order and several asked my wife if I had any unmarried brothers...or eve cousins.

Reading material. Light hearted stuff. Jerky and have a source for jerky as well. Get your own Magazines. While those with tan followers are good they are not as good as what you can buy.

A portable water heater, shaving with hot water is always good and for my ramen noodles

A 5 gallon bucket with lid. Makes for a great stool and protected storage unit. Also fits inside a duffle bag. Best thing I ever toted around the world with me.

Woobie,porn,baby wipes, duct tape, gambling cash, stamps, rosetta stone language(Arabic), laptop, hot plate, last letter, dip(to sell or dip), usb controller for NES emulator