Had the same question 5 years ago when my airline was about to go out of business. Here's what I did, worked well:
Get an insurance license and sell life insurance. It's a product that many people need, and those that do have it are typically paying way too much. It's simple, pays well, make your own schedule with clients. At the end of the day, like anything else, it's sales, so if you can't stomach rejection, go pick up shifts at Burger King.
Our typicaly policy is a term policy with an $800 premium. To make the math easy, let's use $500 as a typical premium. Almost always I write one policy on the husband and one policy on the wife...wala, average $1000 premium per couple. I make 70% of that or $700. Do that a few times a month and you got some extra pocket change.
And yes...I'm an independent broker, so I can shop any company, no sales quotas, no sales managers to answer to and I own my book of clients. I went on to get an investment advisor license, so all of my old insurance clients have become investments clients. And no, I don't manage their money - I hire a third party money manager to do it and I charge 1%. The name of the game is assets under management - $10,000,000 pays you about $100,000 a year - is that enough extra money for you?
So, soon I will no longer DEPEND on flying. I flew all while building a book of business and within the next 3 to 5 years I'll go full-time contract (cause I do like to fly, just not on a choke-chain schedule).
WARNING: This route is harder than most, but it's also worth it more than anything else. PM me if you want more info on what/how I did it.
AZ