I got some good advice from an NCO when I was an E3 and told to keep a copy of every promotion order, pay stub, training order, etc., I ever got while on duty. I still have over 95% of those.
I used to work for a COL and when we asked him if we could throw documents away, he’d say “Just make sure you make a copy and send them to the historical records section”.
I had an uncle, KIA 1944 in France and is buried in Epinal an American Battle Commission Cemetery. It took me almost three years to get most of his records. I will help anyone for free if you PM me. In the meantime, did your loved one survive the war? Did he ever go to the VA? Do you have his ASN, if not you can possible find his enlistment record online, at the National Archives website. You can contact professional research companies. This is not cheap, I was quoted $200, a one page record. Was he KIA? If so the VA may have a file which provided mucho info.
I got the same advice from a WO3/4? at BCT Fort Dix...2d or 3d day. Excellent advice and I kept most everything for 27 years.