Here's probably my favorite global ignore pattern:
/scratch
in any repo I can just create this directory (or instruct the agent to) and then place all my stuff that I don't want git tracked (examples, draft plans, posts, etc)
Ever add a personal scratch file to .gitignore just to keep git status clean? 👀
Don't change the shared .gitignore for something only you need.
Use .git/info/exclude instead.
Same ignore syntax. Local to your clone. Never committed.