what ideas would be possible to do for a mini company idea?
ANYTHING, think of something to do with your interests or talents - that's the closest I could give without giving away my idea lol.
The whole point of mini company is to come up with your own idea that's authentic and unique. You really need to think outside the box to make your idea/product interesting while still achievable. I think making it doable and efficiently doable is key to it being successful.
I haven't mostly because people don't bother with it so they never got a chance to succeed from the start really. It's a worthwhile project if you put in half an effort. My team of two didn't win anything but still made a nice profit of over 500 euro between us!