Pre-scran-scran is a meal eaten before the main meal. It might only be a snack, or it might be a more substantial.
Pre-scran-scran is by nature a savory meal and not a sweet like pre-scran-duff, or post-duff-duff
Pre-scran-scran in its most significant form could be an entire meal such as a box of chicken legs and fries eaten before your curry.
In a lesser form it could be a tube of pringles, some salsa and guacamole.