For simplicity sake to anyone showing up after awhile, for 18.6..
Download the attached save file there ^ and make sure the file name is 1-1-LT1.save
Download the linked persistent file there ^
Once in Summertime Saga, run it and save once, then replace both files under /save file folder of the game and then copy both files into your AppData folder, following the post here:
https://f95zone.to/threads/summertime-saga-save-request-thread.15428/page-17#post-1890771
Once both locations have the same 1-1-LT1.save and persistent files in them, run the game, load the file once and then move about or something in-game, save over to make sure it stuck, then you can leave to the Main Menu and the Cookie Jar will be completely unlocked.
Hope that helps, totally forgot since 17.0 how to do this.