I would carry what the person protecting my back was carrying. Shared ammo, magazines and parts.
As a solder which I am not (X Navy) and have no idea what going into harm’s way is like? I would want it to be the best weapon that money can buy. Supplied with the best ammunition money can buy and given all the ammo I can shoot to become better than any opponent. And I would want the people paying for it all to appreciate where their money is going.
Other than that, I really wouldn’t care what it was.
"The difference between stupidity and genius is that genius has its limits" Albert Einstine