If I take my car in for a coolant leak and they find a laundry list of stuff including the gas cap I would start questioning things. If you asked for a full inspection or mentioned other issues that's another story, but the gas cap - really?? How did they find it defective in the process of looking for the source of a coolant leak??
None of these are rare failure points as the miles accumulate, but it's a big list if all you took it in for was a coolant leak fix. You must be frustrated if all these issues were unexpected.