I love the starting menu's color palette and design! Looks lemon-y.
The pixel art sprites were nice too. Didn't encounter any bugs.
Feels like a good prototype to build further on, some of which you already identified (e.g. addind sounds, more enemies, perhaps more types of drink even).
Also.. profit margin of $0.25 on one lemonade.. :( .. im gonna have to sell until im 300 years old to retire.