When you complete the game once this feature will become unlocked. In New Game+ mode you begin a new playthrough with your previously earned inventory and resources. The following is a list of things that can be unlocked in New Game+ mode.
Unlock +3 Clip Circuit Set: Beat the game on casual difficulty.
Unlock +3 Damage Circuit Set: Beat the game on impossible difficulty.
Unlock +3 Reload Circuit Set: Beat the game on normal difficulty.
Unlock +3 Speed Circuit Set: Beat the game on hard difficulty.
Unlock Builder's Circuit Set: Collect ALL 12 Blueprints.
Unlock Comms Circuit Set: Collect ALL 36 Audio Logs.
Unlock Crafter's Circuit Set & Deep Dig Suit: Collect ALL 73 Weapon parts.
Unlock Devil Horns: Beat Classic mode in New Game+.
Unlock Earthgov, Unitology, S.C.A.F., and Alien Circuit Sets: Collect ALL of the specific set of artifacts.
Unlock Engineering Suit: Beat the game on any difficulty setting.
Unlock Flight Suit: Collect ALL 40 artifacts.
Unlock Hostile Enviornment Suit: Finish ALL 10 optional missions in Co-Op mode.
Unlock Mega Resources Deposit: Beat Pure Survival mode in New Game+.
Unlock Mk-II Overclock Parts Set: Beat Pure Survival mode in New Game+.
Unlock Mk-II Overclocked Attachment Set: Collect ALL 61 Circuits.
Unlock MK-II Overclocked Frame Set: Complete ALL 10 optional missions.
Unlock MK-II Overclocked Module Set: Collect ALL 71 logs.
Unlock Mk-II Overclocked Tip Set & Flight Suit: Collect ALL 40 artifacts.
Unlock Research Circuit Set: Collect ALL 35 Text Logs.
Unlock Retro Mode: Beat Hardcore mode in New Game+.