Revealed is a nickel plated engraved M1911A1 pistol with spare magazines. A Nickel M1911A1 is the primary weapon of Baby Doll (Emily Browning).
Flintlock Pistol
During the trench battle with the World War One German Zombie Soldiers, Rocket (Jena Malone) uses a combination of bayonet and single shot flintlock pistol. She uses the pistol as a club in hand to hand combat, which is probably the most practical use for the antiquated weapon in that battle.
Remington 870
In the battle with armed automatons, Sweetpea (Abby Cornish) uses a tactical Remington 870 Shotgun with surefire light and door breaching muzzle.
Looks more like a Colt 1860 Army with a Richards conversion. Note the rear sight on the frame ring, not the hammer. - Gunmaster45
Lewis Gun
Unidentified Carbine
In what may seem like an anachronism, in a film filled with (intentional) weapon anachronisms, a zombie German World War One Soldier attacks Blondie (Vanessa Hudgens) in the trench with a rifle that has its bayonet mounted. German soldiers from WW1 would be issued the Mauser Gewehr 1898 rifle, but this is far too short to be even the anachronistic Karabiner 98k.
Modified Mini-Gun
TBD Weapons
In the battle with the robots, we see heavily modified weapons which look like they may be based on real world guns.
M249 Para Model
What looks to be a paratrooper length M249 with rails is seen being held by an older man (Scott Glenn) dressed like a British World War One Officer in a promotional photo from the production.