Every time you make a new beverage in Starbeans Cafe, Professer E. Gadd (last seen in Luigi's Mansion for GC) comes and samples the drink. Afterwards he gives you a special item.

Drink 1: Greed Wallet (doubles the coins you get in battles)
Drink 2: Bonus Ring (doubles EXP if taken no damage)
Drink 3: Excite Spring (floating defensive jump)
Drink 4: Great Force (doubles the damage you give and receive)
Drink 5: Power Grip (don't lose hammer in defense)
Drink 6: Cobalt Necktie (doubles your 'stace points)
Drink 7: Game Boy SP Horror (get rare items easier after battles)