Okay, it’s countdown to the end of the year, and you haven’t fully funded your 401k with the maximum amount of contributions.
What can you do? March down to your Benefits department or Human Resources and ask them if they will allow you to put in a lump sum contribution before year end to make up the maximum 401K contribution that you are allowed based on your salary.

Believe it or not, many employers will allow you to do so— but you gotta ask. So get down there and make the maximum 401K contribution that you can (and enjoy that extra in your tax refund amount).