My degree is in biology, and my career is a software developer. Initially as a programmer, now as a Business Analyst and Project Manager.
I hate to say it, but if I were you I would not get a job in the anti-religion field.
The problem is that this field doesn’t pay much first of all, and secondly it could make getting a different job more difficult. That is unfortunate, but true.
If your only job on your resume is from CFI or FFRF, etc., then that might make getting a job at a school difficult, even if it is not supposed to, or anywhere really.
As for writing articles, the market is growing progressively worse due to the Internet. Be prepared to do a lot of writing for free before getting a paying job at it, and then be prepared to get paid pennies on the hour basically.
Do you know any foreign languages? It could help if you knew Chinese, Spanish, German, Japanese, or Russian. That could make getting teachings jobs much easier, teaching English as a foreign language classes, doing translations, or teaching in a multi-lingual setting, etc.
Do you belong to any professional organizations? Do you have a blog?
If you want to write having a blog now is a good idea, one that is geared toward a popular audience, not religion bashing, etc., but one you can present as a portfolio of work to an employer.
I think that a lot of what people do with your degree is start out in editing, proof reading, etc. Be prepared to proof read math textbooks, etc.