There are five inventory items that Duke can carry in DNF. He can only carry one of each.
Dukevision[]
Duke Vision in DNF acts the same as the Night Vision Goggles in Duke Nukem 3D, allowing Duke to see in dark areas. Duke will always have Duke Vision with him, as it is built into his sunglasses.
Beer[]
Beer will make Duke stronger and more resistant to damage for a short period of time. However, Duke will get drunk and blur the player's vision.
Holoduke[]
The Holoduke returns in Duke Nukem Forever. It will run around and distract enemies as well as cloak the player. It will also comically misinterpret Duke's classic one-liners in a robotic voice. (Ex: "I am here to chew bubblegum, and kick ass. And I'm all out of ass.")
Steroids[]
Steroids also make a return in DNF. When Duke takes steroids, his speed will increase and his Melee damage will increase, but the player will be limited to punching and Duke's ego will decrease by a quarter.
Jetpack[]
The Jetpack in Duke Nukem Forever is only available in Multiplayer mode. When the player gets the Jetpack, they may fly around the level until they run out of fuel.