I have one initial ‘package’ for personal training with is introductory and consists of 3 sessions plus an assessment. This package is pre-paid.
Subsequent sessions are billed monthly. Thus I do not run into the issue of whether sessions expire or not. This is working very well for me. Large packages can be very expensive. This method necessitates a conscious decision to every few months. The monthly billing ensures a steady income flow and has helped me with remarkable client retention.
Hope this helps.