Charbucks mentioned mustard.
Me and a friend of mine used to eat pilchards on toast:
And the funny thing was that each time we ate one we dared each other to put more and more mustard on top.
WARNING: Do not do this if you are suffering with sinusitis. The mustard will go up into the cavities of your skull and make you feel that your head is on fire. I mean it. Really. I nearly started crying because of the pain.
So anyway, pilchards on toast with mustard.