There's a trainer mode you can access by getting a high score of over 1,000 points and dying. Now enter "LOVEBUNDLE" for your name in the high score table. After you press 'Return', the message: "PASSWORD ACCEPTED. TEST MODE ACTIVATED." will appear letting you know the cheat mode is activated. Now press 'Return' again and delete a letter from the word "LOVEBUNDLE" and again press 'Return'. Next press 'Space' to restart the game. When the game starts, press 'P' to pause the game. Now press 'F10' (do not hold it) and enter the following sequence (The dash is on the main keyboard.):

Once you press the last 'E', the game will start to load. You'll now appear on level 2 with infinite lives and all the weapons. If the game unpauses while you're typing the last sequence in, pause the game and retype it. If you pause the game, press 'F10' and type it again you will go to level 3.

There's a force field in the second cavern, that seems impossible to get rid of. To get to the time machine chunk beyond it, simply fall off the right side of the phone booth platform above.

Here're all the coordinates of all the jetpack platforms, in the order you should go to them to finish the game. X/Y, X being width and Y being height: