Mostly WW2 and above although some rifles/pistols span several wars and also I go for different variants/models of each. Then I go for bayonets for each and the various variants/models of those.
Then different do-dads of various equipment such as cartridge belts, fighting knives, original ammo etc.
My father (also a Marine) got me into it and its been our "together hobby" since I can remember.
That's awesome. Thanks for your service!
When I was a kid, I could spend hours in the Army/Navy surplus store just pouring over every item.