How To Unlock All Shop Items: There are some unlockable items hidden in the in-game shop. Instead of finding them in the levels you unlock by doing random tasks like going Game Over, finishing the game's story mode, by playing Mega Man 11 on a Saturday, etc.

Awakening Chip and Cooling System Infinite - Beat Dr. Wily
Buster Plus Chip - Fire the Mega Buster 500 Times (250 on Beginner)
Capsule Catcher - Deplete a special weapon's energy or Rush energy 30 times
Cooling System - Use the Double Gear System 100 times (50 on Beginner)
Energy Balancer Neo - Buy the Energy Balancer
Energy Catcher - Get 10 Game Overs/Play the game on the Beginner difficulty
Pierce Protector - Get killed by spikes 5 times
Power Shield - Take 200 points of damage in total (100 on Beginner)
Screw Catcher - Set the system's clock so that it's Saturday
Speed Gear Booster - Use the Speed Gear at least 50 times (25 on Beginner)