Below are listed various suits and masks not available from the beginning.

Unlockable	How to unlock
El Diablo	Complete the game on any difficulty.
Elliot's First Chapter	Complete the game on any difficulty.
Elliot's Original	Complete the game on any difficulty.
Meat Armor	Reach level 25.
Meat Man Mask: a distorted face of... meat.	Reach level 25.
Tyson's Bronze	Complete the game on any difficulty.
Tyson's Final Mission	Complete the game on any difficulty.
Tyson's Original	Complete the game on any difficulty.