Apologies for the necro, but wanted to add some additional information as I had the same question.
First, create a new folder in the “Content” directory of your project. Then, move your .sav files to the folder via your computer’s file explorer.
Next, go to “Project Settings → Packaging” and at the bottom of the “Packaging” section, click the down arrow to look at the advanced settings. Here, look for “Additional Non-Asset Directories To Copy”. Click the “…” button and select the aforementioned folder.
Now, when you package the game, the files will be copied to the “Content” folder of your packaged game!