Regarding experience with donation boxes:

Our very small museum has found  donations are more abundant on weekends
and when the box is salted with bills. . .foreign bills help. . . people
are intrigued enough to comment, and once they admit they have noticed the
box they almost have to add to the pot or feel embarrassed.  We have used
the same batch of foreign bills for years. The amount donated is directly
proportional to two other factors as well: the exhibit's degree of
relevance to the visitor and to the degree of friendliness of the museum
staff.  Visiting Museum professionals are the most generous donors of all.

Carol Morgan
Demuth Foundation, Lancaster, PA