All of the items are turned in, especially sidearms and body armor. A Kevlar helmet would prompt a Report of Survey, but since it is under the $250 limit under the pamphlet, it would not have been submitted to the IRS for collection. Electronics like sidearms are part of the MTOE and would never be "given" away. A missing sidearm would prompt an AR-15 investigation and could result in criminal penalties.
And that also depends... records get lost, etc.
I ended up with a full set of winter outfit - field jacket with liner, gloves, winter coat, insulated pants, boots - they had been issued to me when my squadron was deploying aboard ship - at that time we were in MAG-13. When we returned from that 6-month cruise to the Indian Ocean, MAG-13 had moved to a different base, and our squadron had been transferred to MAG-11. All of our supply records etc were supposed to have been transferred, but....
When I was discharged, I went to supply to check out - I had all the gear in my truck. However, Mag-11s records showed I had nothing checked out, so I said nothing and kept the gear.
Additionally, the weapon you muster out with might not be the one you had been assigned... it could have belonged to a casualty and got written off as "lost in combat" (especially if the troops had to withdraw from the battlefield under fire), or could have been a "battlefield pick-up" of an enemy weapon. While it is much harder than it used to be, even in Afghanistan & Iraq our soldiers managed to get approval to ship home (or carry back upon return to the States) many older weapons, especially those from earlier wars in those places (I have seen a lot of pics of Martini-Henrys & Martini-Enfields from the 1880s-90s, and Enfields (& Mausers, Nagants, etc) from WW1 or 2 that were seized or bought from civilians in Afghanistan that were approved for shipping back as private items).
The same with body armor... a lot of civilian organizations purchased body armor and shipped them to our troops when there was a shortage - they were never part of the military supply chain, and a good number of them came back stateside to soldiers' homes.
Or many other such irregular and undocumented (or even approved) ways to acquire equipment that you are not required to turn in when mustering out.