The following is a list of all the items which become available when you reach a certain level. Once you reach level 13 and can obtain the Legendary assault rifle ("Warrior Assault Rifle") you will be able to obtain all in-game items (if luck is in your favour).
Stufe 2
Stufe 3
Stufe 4
Stufe 5
Stufe 6
Stufe 7
Stufe 8
Stufe 9
Stufe 10
Stufe 11
Stufe 12
Stufe 13