During play press 'P' to pause the game. Now hold down the 'Left' mouse button and press 'F1'. The background should change to green. Now unpause the game and use 'N' to advance levels. To shut the cheat off, repeat the previous instructions.

Start level one, take out the disk and insert disk number 2. Let all your time run out and you are taken to a much later level, after the chest bursting bit, no matter what the brief says! On the level after this one, at the top right before the exit, there's a platform full of medipacks. Climb the ladder that seems to go nowhere. On the level after that, go to the bottom left for full everything.