Archivo de actividades extras en caso de necesidad

Archivo de actividades extras en caso de necesidad
 

Se diría todo eso back-up file también?

Sí. But you may want to specify that the file contains extra activities.

File of fall-back activities, perhaps.

An extra-activities back-up file. ?

:thumbsup:
'Fall-back activities' fits nicely, especially in the sense of having something else on hand if the chosen activity won't work out (due to inclement weather, if some students are missing, etc.).