Get Desired Cards
To change cards in your booster packs, check your booster packs at the card keeper. If you aren't satisfied with your cards, just reload to find random, new cards in your booster packs.
Digivolutions
Reach Level 16 with Guilmon to teach him Agumon digivolution technique. Reach Level 16 with Agumon to teach him Dorumon digivolution technique. Reach Level 16 with Dorumon to teach him Veemon digivolution technique. Reach Level 16 with Veemon to teach him Guilmon digivolution technique.
Digivolution with 1 HP Remaining
To get a Digivolution by ending a side quest with 1 HP remaining, go to the Goblin level. Take a "gate disc" with you. Go to the area after the rolling barrels and fall into the space between the two sides. You are automatically be revived with 1 HP. Use the gate disc and return to the base. After you return with 1 HP, save the game. Go to a side quest that requires having 1 HP remaining to get the digivolution.
Unlimited Bits and Items
Start a game with two players. Give all the bits (or items) to Player 2. Then, save Player 2's progress at the save keeper. Have Player 2 give all the bits back to Player 1. Quit the game with Player 2 at the save keeper without saving. Then, have Player 1 to the call keeper and rejoin Player 2 with the same Digimon. Repeat this process for unlimited bits and items.