Companions, specifically Boone, will randomly drop weapons when they run out of ammo. Actually the weapon is specific too, the CZ57 Avenger.

The companion weight glitch. The weight glitch that i actually have grown to love will let you put unlimited items on your companions. take Boone for example, his total holdable weight is 250. Fill him up to say 245 then give him a heavy item of about 15 or more weight. Once you get over the 250 threshold, you can begin giving him low weight items like ammo and such too. You have to do it all at once, if you exit the inventory screen you have to start over if you want to add more weight, meaning unloading him to about 245 again and giving him a heavy weighted item.

Can anyone confirm these?

No, can't confirm the weight thing. I travel light, use the safe in Novac and my Goodsprings home (a mod).

I can confirm that Cass keeps switching out her rifle and opting for the knife. This only seemed to happen in New Vegas Square.

Not sure if that's a bug cause in FO3 if a companion ran out of ammo it seems they trashed the weapon