You can store it on a server.
Or just not worry about it. I actually prefer games where I can easy modify stuff - I generally play through normally first and then go crazy with cheating a second time. It’s fun to do. Let players make their choice and just give the file a different extension so that text editors won’t automatically open it. Most players won’t bother looking into the save files.
Hi, i have the same question, what is the best method to store something offline on a local machine? i mean the classic savegame, or just a character data sheet, without using online methods and obviously without storing it on a .txt file. Should i create a file with custom extension? or the is a way to have a local DB?
Didn’t we just discuss this very question? Read through the thread, decide as to how far you want to go to stop people from changing your save files and then go from there 
Mike
I don’t think DB was mentioned. Obviously you can use JDBC and then use Oracle with PL/SQL or Mysql DB for a game aswell.
Sure, but that’s even less secure/stable than the text file option
Mike
I almost always just use SQLite. It’s simple, it’s structured, and if someone wants to cheat … who cares? As long as they have fun.
This only really matters with competitive data (highscores sync’d with a server and whatnot), but “securing” that is a very different topic.
It depends on how far you want to go. If it’s a single-player game, and not online, why should players not be able to altar their save files? Does it harm the game, for you?
If you just save the information in a file, but use a binary format instead, humans wont be able to read it. However, no matter how much you encrypt and zip the files, you’ll at some point need to de-serialize it, and there’s nothing stopping people from decompiling your source code and looking how you’re doing it. If you can do it locally, so can they.
Consider if it’s worth it.