I'm not sure what specifically to say about this....you get all your W-2 forms together in say, February or March, then prepare and file like you normally do. IF you had a regular W-2 job before deploying, you'll need that too.....just like normal, you cannot file until you get ALL your W-2 forms from DFAS & any civilian jobs you had before being activated, along with any other tax forms tam include interest and any investment income too.... If you are still deployed, hopefully someone at home in KS will collect them together for you, or perhaps you are having all your mail forwarded to you It's just that you will have more income this year from NG and DOD together.......but probably less from that civilian job.
Since the border is not an official war zone, you cannot claim the active duty pay was Combat pay....of course, if it was your DOD W-2 would show it that way...but it won't.
And all the deferred SS taxes were not deducted from your military pay those last months of 2020? Those SS taxes will be deducted from your 2021 pay during Jan-Dec of 2021, so you might see a drop in your pay going into this year. (Though the last DOD budget bill increased pay some 3% for 2021, so it's hard to guess how that will balance out until you get your next few military paychecks in 2021.)
Unless you have something specific to ask about?.....more Sr NCO staff, who have been activated before may have a better idea about specific questions you may have and how it may apply to your current deployment.
Of course, thee may be some NG members deployed to the border in prior years who may have some insight and recommendations about specific activation & deployment situations that they had to handle in special ways when dealing with their taxes.
Assuming you're a Kansas resident:
"The active and reserve duty service pay of military personnel is taxable ONLY to your
state of legal residency, no matter where you are stationed during the tax year. If your home of record on your military records is Kansas, and you have not established residency in another state, you are still a Kansas resident and all of your income, including your military compensation, is subject to Kansas income tax."