The contents of the .git
folder itself aren't very dynamic (what changes rather unpredictably are the refs and the logs, so just stay away from them).
If you take a look at the .git
folder of any of your repos, you'll have a pretty good idea what is usually there.
AFAIK, folders in the top level of the .git
folder do not usually start with a period, so you could just make a folder .git/.scripts
to contain your private script files.
If you want, you can also make that inside the info
folder -- that's really up to you and which you find more orderly.