When you view a generic booking* in the planner you will see that those items are shown in purple.
Here is an example of looking at a generic booking with 'view Planner'
you can see that each Item (even though it has not yet been allocated a specific Item) are shown in purple.
Each row also has the activity (relating to this reservation) represented - in black because it is provisional;
Here you can see we searched for new reservations, and some of the results were generic bookings, so when I choose Day View then any generic Items are shown in Purple;
* a reservation containing one or more Product Line - rather than Item.