Freelance tutoring? Depending on how often you actually get called when you're on call, you could set up a regular weekly tutoring appointment with the understanding that some weeks you might have to reschedule at short notice.
Also, try to think of tasks where the customer doesn't much care exactly when it happens. Yard work comes to mind. Or jobs you can pick up from the customer to do on your own time: scissor sharpening, sewing alterations.