Adding text box info to a list picker to be saved after app is closed

The Image shows what I have so far, I have it working that when the user enters the drink size it saves it and stores it in list picker, and is saved there after the app is closed down. What I would like some help on is that with this setup I can only and 1 size and every time a new size is entered it overrides the previous input instead of just adding a new value to the list picker.
Any help with this would be greatly appreciated.
Thanks in advance.

A post was merged into an existing topic: Adding text box information to a list picker permanently using TinyDB1