How To Unlock All Post-Game Shop Items: There are some unlockable items hidden in the in-game shop. You unlock them by finishing the game's story mode to the end (beat Dr. Wily), at which point they become available to buy at a price of 3000 Bolts.

Awakening Chip [Infinite] - Infinite Weapon Energy for completing the game
Cooling System [Infinite] - Infinite Double Gear Time for completing the game