When I bought DNF I got given a card with a code for Dukes Big Package which gives you some exclusive unlockables.
It says to enter it in the Extras Menu. I have now finished the game and unlocked the Extras menu, but still cannot see where to enter the code.
Not a big problem, but would be nice to know.
Also, the cheats that you can unlock via the Extras Menu, lets say invincibility for instance, if you enable them, do they disable achievements?