Choose your work carefully. Often, freelance positions offer more of the flexibility needed. Jobs that have portions that can be completed in the car while you wait are often helpful.
Flexibility is key.
Break each job into steps, with quickly reachable goals. You cannot often complete one whole job in the bits of time available but often you can break the job into workable steps. Resist the urge to be overly optimistic about the work hours available to you - always budget your time assuming emergencies can and will happen. Don't wait for long periods of open time, learn to fit some work into five-minute lulls. It is also helpful to learn to work in odd environments.