Enable the console from the game's in-game options. Hit the ~. Type
seta thereisacow "1337"
then press ENTER. Then type
spdevmap eldaba
then press ENTER. This will start the demo with cheats enabled. When playing, drop down the dev-console and enter the following codes and hit ENTER to activate or toggle them.
Result
Cheat Code
give all
Each time it's entered you'll be given 2 different weapons from the demo.
