Cheats
Within the game, type:

F12-F1 = Restore Health
F12-F2 = Get all Weapons
F12-F3 = Get Shield
F12-F4 = Win the Game
F12-F5 = Get Fuel

Another way to get weapons, health, shield, and fuel is to hop on the back of a Pteranodon and ride him up
high in the sky. At a certain altitude you will be given all the free stuff.

All items and health
Find one of the mountains on level 1 and jump to the top. Then, jump as high as possible. At this time 100% health, all weapons, 999 items, a full jet pack, and shield will become available.

Double jump
If you double jump off a mountain, you will get a shield and fuel.