Early round you literally just need the bowing knife to survive, up until like round 12 the bowing knife one shots which is well over enough time to get perks and the mp40 which is probably one of the best wall guns.
@Thatcheeser Trench shotgun is way better, one time in Der Riese I joined a game on round 20, obviously I had no perks nothing so when i got 1.5k, i got the trench. And oh my god, It only took 2 hits to the head for the zombies to die, keep in mind I had no double tap root beer... Trench is S tier weapon.