I don't know if it will be possible to do where you are, but I mowed lawns for years on the side. Even after I had a "successful" startup. I enjoyed having something completely non-technical to do and it actually let my mind reboot. And before anyone scoffs, the pay is actually pretty decent relative to the time invested. Don't believe me? Call up a landscaping service and get a quote for your yard. There is some initial costs for equipment, but it's definitely something that is scalable. You can get a used lawnmower for less than $50. It doesn't have to be great, little push mowers are work horses and damn near indestructible. Especially anything with a Briggs and Straton Motor. But like I said, this will only be relevant if you live in a part of the country you can mow lawns in.
And on your comment about working in a cafe. I have often thought about how great it would be if someone started a "Startup Cafe" with a rag tag group employees that were all working on their own projects. Somewhere you could pick up a few hours in your odd spare time and still be in a stimulating environment. Maybe have a laptop setup next to the server stand for a few snippets in your downtime. Someone start working on that! I'll buy my coffee there.
I had an idea for a "carbon-free lawn service". The idea was to get together about 10 people with the push reel-type mowers, lawn and hedge sheers, and develope a route that could be done by bike. One of the group's garage would be the central meeting place and tool storage spot.
I would seek out about a dozen clients who cared about carbon and hopefully had small lawns, rich aging hippie types. I would charge about twice what normal lawn service costs; the whole group would arrive and cut lawn and do any other work en masse, otherwise I think it would take too long.
The overall goal was to have enough work to have 1 full day's hard work each week, for which each person would earn about $200. I wanted to design the business explicitly to provide a way to pay the cheapest rent in my area (half the cheapest two bedroom apartment) and a little left over for food and etc.
I wish someone would try this. However, the person who actually starts it for the first time will probably find themselves working full time for quite a while, and it won't be a part time backup job for them.
A side note on lawn mowers -- they are almost all not work horses or indistructable, particularly the $50 ones you will get used. They are garbage. Briggs and Stratton has a good reputation, but I am not sure they are currently living up to it. A good rule of thumb is to get the best ratio of engine displacement to cutting swath you can get. If you get the used ones, get three and expect to be constantly repairing them, which will be fun for a while and then get old.
I like the carbon free lawn service idea. My current mower is actually an American lawn reel mower. Coincidentally, I bought it on craigslist for $35. It's from 72, and still cuts like a champ as long as your willing to maintain it. The "carbon free" service would work great in my area where there is a high density of people in town homes with small front lawns.
Maybe YMMV on the small lawn mowers. But I have had extremely good luck with them. I think that most of the problem people have with mowers is failing to maintain them properly. In my experience, if you can buy a used mower that will start quickly without much hassle it can generally be kept in decent working order for a long time. But purchasing one of these used mowers was why I said the idea scales. It's pretty easy to get enough work out of a used mower to buy a better quality mower.
Thanks for sharing your insight. I hope someone jumps on the reel mower service.
This is a good point, here in San Diego (Normal Heights) there is a coffee shop called "Lestats" and all of the employees are in the same band... They work there and play in their band - kind of cool actually.