I joined my company 3 years ago as a subcontractor working 2 days a week. I stayed on after the project with other production tasks, as well to operate a new piece of equipment, and started working the full week.
Months later a part-time staff in a managerial position was leaving, and the boss asked if I wanted to take over their correspondence, bookkeeping, and database management tasks. I accepted the offer, and organized my roles accordingly. These tasks usually combine together into a full work week, while otherwise each task would only take half to one work day to do.