That depends on whether the student is an intern or a temporary employee (and whether or not the student is related to a manager

).
In the case of a temporary employee, putting away glassware, sweeping the floor, emptying the wastebaskets, etc. (or whatever they were hired for). If they are enthusiastic and interested in learning, then automated titration, melting point, etc.
In the case of an intern, there is more of a responsibility to provide meaningful experience, even at the expense of productive work. At that point, it depends a lot on the reliability and maturity of the student. Some activities don't require more than manual skills (preparing KBr pellets for IR, for example). Triple-checking calculations in lab notebooks is another possibility. If the student has computer skills, then an internet search is a possibility. If the student is really good, converting repetitive calculations into spreadsheets.
In any case, you obviously have to be careful with anything that might have regulatory consequences.