As a 30-something, I've suddenly come to realize that retirement savings are important, and that small amounts of extra savings can add up. Suddenly an extra $100/week actually sounds worth thinking about.
Are there simple ways to earn a few extra bucks as a developer in your spare time? Or is it just down to 'invent some SaaS offering and hope people like it'?
What simple things have you do that have brought in a small bit of extra income?
As for "dumb" things you can do: cook more at home, pregame before going out, do activities that are cheap or free (eg bike rides instead of theaters), bike more instead of driving everywhere, read library books, etc
(The benefit of these over "do consulting" answers also lies in the added quality time with family rather than more work.)