Went further than lunch!
I have had more than a free lunch. Whilst working at a University, I was tasked with helping with an intermittent issue with the serial port on a workstation used for experimental research. Spent ages trying to figure out why the serial port kept misbehaving, before finally deciding to replace the motherboard (it was an older workstation with built-in serial port, and I had a couple of spares in my storage room). The female post-doc researcher for once seemed interested in the work I was doing, and we chatted for a while as I swapped components around in the system.
After doing this, the system worked fine. The next day, the nice post-doc researcher brought me a thank-you card and a box of chocolates for my time - which was great! I was then invited a few weeks later to play badminton after work with her. One thing led to another, and well - she's my wife now!