Question

If you were to see a couple of inconsiderate people simply abandoning the remains of their picnic lunch on the lawn in front of the campus building in which your archaeology course is being held, you might ask them to pick up their:

Answer 1

You might ask them to pick up their "primary refuse".

Primary refuse in archaeological terms is the undesirable items or materials found in the setting where it was utilized and disposed of.

This is inverse to another term utilized "secondary refuse" which are the undesirable items or materials that are expelled from the site at which they were utilized and are discarded at an alternate area.