Paganinis, more commonly referred to as Pags, are a set of stackable wooden blocks usually about 9 inches square
The grip uses them to support metal track over a uneven surface. For example, if tracking outside on a street, the dolly shot might start on the pavement and then move on to the road and Pags would be used to build up the track to the same height as the pavement.
It's really important that the track is perfectly level and the grip will use Pags, wedges and a spirit level to ensure this.
Legend has it that the name Paganinis is taken from the Italian virtuoso violinist Nicolo Paganini who used to perform with one foot raised on a wooden block which became known as a Paganini.