How to find needed modules for rebuilding kernel

[Pat Maddox]

In rebuilding a kernel, how do you know exactly what modules you need?
 The Handbook is a good start, and a lot of them are obvious (i.e. if
I have no SCSI disks, disable all SCSI modules).  Others aren't so
easy, particularly serial devices, and the pseudo devices.  How can I
find out exactly what I need to enable, so I can make the kernel as
tight as possible?