Some of the things you can do with custom reports:
Create a list of female attendees who are allergic to specific food/food types.
Enter report title.
Enter date range.
Select attendee as user type.
In Associated fields, select first name, last name, email, prefix.
In Filter by, select prefix, select only Mrs. and Ms. since it is only female attendees you would like a report for.
In Custom fields, choose Food preference (This is a custom field and need to be created using the form builder for attendees to fill up during registration).
That's it, and don't forget to save.
Create a list of attendees who have checked-in to the event.
In Associated Fields, select first name, last name, email, check-in.
In Filter by, select check-in, select Yes since it is only checked-in attendees you would like a report for.
Create a list of contacts with birthdays in a certain date.
In Associated fields, select first name, last name, email, Date of birth.
In Custom fields, choose Date of birth and select a date to generate all contacts with birthday on that day (This is a custom field and need to be created using the form builder for attendees to fill up during registration).