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).
Level 2
Level 3
Level 4
Level 5
Level 6
Level 7
Level 8
Level 9
Level 10
Level 11
Level 12
Level 13