Fun fact: there were historical combo weapons. The bayonet, of course, but also many kinds of sword-pistol and knife-pistol.
My favourites however – simply because because they are quite bonkers – are described in Fiore dei Liberi’s treatise: if you look at the “Axe in Armor” section, paragraphs 15-17, you’ll see a poleaxe-bola combo and a poleaxe that delivers a blinding caustic powder.