Depends on where you live and how much time you have. As a programmer, your main skill will earn you more in an hour than most people earn in a day. That said, don't burn yourself out, mix up your skills.

If you drive a Lyft, you could pull in an extra $20/per hour. Do the math as far as what gas and maintenance will cost you.

Can you do pet sitting or house sitting for people out of town? At least in SFBay, that's about $20/hr on Task Rabbit.

You could also give your time away since it sounds like you have available time after your full time gig. It is a chance to meet new people and out of that, though you shouldn't expect it, you could land some side gigs.