How to add multiple files with different extensions to git all at one time…

You can add to git by explicitly listing each file with spaces as delimiters.

$ git add file-name-1.php file-name-2.js file-name-3.html …

The accepted answer is perfect for the OP’s specific case. But I got here—via Google—needing to add multiple files with different extensions. Posting here in case you miss this similar answer to a similar question.

Don’t forget about interactive staging

Git interactive staging can also work wonders. To enter interactive staging (aka: adding, removing files):

 $ git add -i