Simply type in any of these words when playing the game:

Code                      Result 
kablooie                  Huge Explosions 
hammersplease             Max Hammer Power 
zappo                     Win Current Level 
zool                      Get Keys 
medic                     Restore Health 
agua                      Walk on Water/Lava 
barrier                   Shield 

Free Items
     First  you  need  as  much  money as you need to buy the item you
want,  so  fight  a  lot. Go into the shop in the chapter, and buy the
item  you  want,  then  press exit but DON'T move! Save the game right
away,  and  then  load  it  WITHOUT  moving. You will get the item you
wanted AND all your money back!