Hidden Cave:
After buying the Hidden Cave mini-game at the store, go to the practice table. 
Start a game, and point towards where the hidden cave is supposed to appear. 
From the break position, go to the right at about the 2 O'clock position and point at 
the cave located there. If done correctly, you will be able to select the map in the 
following step. Press Start to pause game play, then select the 'Inventory' option 
followed by 'Sub Games'. Then, select the Hidden Cave map. Answer 'Yes' when 
prompted to quit the practice game. You should now be at the Hidden Cave, with a 
treasure chest with money. After reaching it the first time, it becomes unlocked at 
the main menu at the island rock.

Shop Items:

Darts mini-game ($4,000) 
Stuffed Dodo ($2,500): Unknown 
Coconut Shy mini-game ($3,000) 
Laser Sight ($100): Helps your aim. 
HUD Goggles ($5,000): Show ball paths. 
Skeepool mini-game ($3,000) 
Hidden Cave mini-game ($5,000) 
Dropzone mini-game ($8,000)