I did most of my career in the black boot Army, so any advice I could give on gear is going to be quite dated. Plus, I was an 11A/59A (don't worry about what a 59A does. The lowest level they exist at is Division staff.)
That being said: some of the gear will be very much job and unit type dependant. An FSO is going to use different kit than a gun platoon leader or the FDC officer. And an FSO in a mechanized or Stryker unit is going to have a very different set of field gear than one in a light unit, because the light guy has to carry all his gear, while the other two have vehicles.
As far as general preparedness, know how to do your job if all of the electronic gizmos (AFATDS or whatever finally replaced it, GPS, etc) ALL fail. Now that the Army is doing warfare against peer and near-peer competitors again (high intensity conflict, as we called it back in the day), you have to be able to operate with your systems degraded or denied, because the Russians and ChiComs put a lot of effort into electronic warfare and other ways to screw up our fancy systems.
Back when I was a company grade officer, I always loved seeing our mortar guys training on doing firing solutions by hand, on paper. We had one particularly awesome 11C NCO who could use a slide rule.
So maybe get a slide rule and learn how to use it. (I grew up around lots of nuclear and electrical engineers, in the 1980s. They all went to school in the 50s and 60s and could still do their math with slide rules, even though they'd been using TI calculators for years and years. I have a good friend, retired FA officer, son and grandson of retired FA officers, who can still do firing data with a slide rule, and he retired in 2000. Although he needs one with larger numbers now days.)
