ToeJam & Earl.

 No.  Code  Effect
   1  MWPA-AA5J  Don't use up presents in inventory
   2  ALKA-AA4Y  Always share presents (even on different levels)
   3  RF8A-A6T2  See the entire map uncovered on each level
   4  REFT-A6YL  Don't uncover any map tiles
   5  GC8A-AYZT  Infinite lives
   6  CJCA-CA6L  Getting youched doesn't hurt you
 NOTE - game may freeze if near or in water!
   7  AL3T-CA6A  Getting squashed doesn't hurt you
   8  HC8T-AA32  Don't drown in the water
   9  HTTT-EA96  Mole ignores you
 10  C5AA-CA4T  Tomatoes fly like slingshots
 11  ATXA-EA3Y  Santa is easier to sneak up on
 12  GBLA-DJY8  Each BUCK found is worth 2 bucks
 13  GBLA-DYY8  Each BUCK found is worth 5 bucks
 14  HTFA-DBSN + DEFA-CAHR    UN-FALL present always takes you up one level  
 15  JC6A-AH6Y  Faster progression through the ranks
 16  TD2A-AEAJ + 6D2A-ACAN  ToeJam and Earl move twice as fast
 17  CB8A-DT2Y  All monsters are boogymen (extra hard)
 18  AZ8A-DT2Y  All monsters are wahinis
 19  CV8A-DT2Y  All monsters are Santas
 20  A38A-DT2Y  All monsters are bees
 21  CK8A-DT2Y  All monsters are moles (very nasty)
 22  1V9A-DCCJ + AF9A-CACL  Kill all monsters with one tomato
 23  5V3T-CLGR  Super hi-tops last 2x as long
 24  4B3T-CRAE  All other presents last 2x as long
 25  RH6T-C6VN + JH6T-DJV4
 + TH6T-DRB6
 Short game
 -you can find all the pieces on the first 11 levels!