Tags for iTunes and Foobar

After messing about for years I have decided to use only MP3 tag for tagging, iTunes for organising iPod Library and Foobar for general playback.
What tags are absolutely required for efficiency of use of these two players?
Currently I am using mp3 and m4a files with a mixture of albums (shop bought compilations, home produced compilations and regular albums).

Thanks

I would say: those fields that you find in the tag panel by default plus ALBUMARTIST and COVER.
I would delete COMPILATION and any other field that is exclusive to iTunes like itunnorm and stuff.