1. Liberator shottie, it's not a ww1 gun but a nam gun, but I feel like you could still have it because it's just like a blunderbuss or a really powerful shotgun, It's a shotgun with four barrels that would use cartiage packs to load into it, if you want to see a pic I would be happy to show one.
2. The Lewis LMG, it was one of the most commonly used larger machine guns in the war on Belgium, personally I feel the game could use another LMG that could be gotten easily than the one from Kara's quest, just throw some dirt on it and name it something like the Jenny gun and bam you got another weapon.
3. Luxtion arsoual gas, it's already in the game have her sell some.
4. The Kolibri 2mm, either as a joke weapon or a weapon that does mad criticals for a smuggler, the Kolibri is a gun that could fit in the palm of a person's hand and fires tiny 2mm bullets.
5. Maybe a colt 45 or an oversized revolver that fires just crazy big bullets or maybe another flamethrower that's better than Kattom's mk2 flamethrower
6. I'd suggest a mortar but I don't think you can get that crazy with the weapons, how about a Mosin nagant sniper?
7. If we ain't got Bayonets throw them in, right with the trench clubs
8. molotovs, grenades, sticky grenades, dynamite or something like it.
9. Maybe some partially damaged Flack jackets to sell for protection
10. M18 automatic, one of the guns I just remembered it's an automatic rifle with big drum attacthed to it
11. Gas mask, just in case someone tries to gas you