First of all, you should be aware that there are potentially many dozens of files involved in building a single package, and that is especially true for building a complex package such as the Linux kernel.
You can get much more information if you pipe the output of 'bitbake -e foo' to a file and then analyze its contents. Something like
$ bitbake -e virtual/kernel >kernel.env
For example, early in the output, you can find the list of includes as bitbake scans and reads the chain of class files. Also very useful, though not directly related to the question is that you can see the cumulative changes made to variables as these include files are read in and parsed.
If you isolate those lines that set variables, you can effectively build a list of files involved in the building of the package. Something like this:
$ cat kernel.env | egrep '^#[ ]*append|^#[ ]*set' | cut -d ':' -f 1 | awk '{print $3}' | sort | uniq
...should produce a list of bitbake files (*.conf, *.bb, *.bbclass, etc) that are involoved in building the package. Ugly, but it works ;)
You might also consider joining #oe and #yocto on freenode IRC where lots of really smart people hang out that know much more about this stuff than I do! Good luck.
