Top four, I'm talking 'dinner dinners', where gravy is always present...
Lamb - mint only.
Pork - English Mustard/apple sauce.  Stuffing.
Beef - English mustard/horseradish
Chicken - No condiment.  Stuffing.
Ham - Mustard/Cheese sauce. NO GRAVY.
Shepherd Pie - Mint and or gravy
Cottage pie.  Gravy OR ketchup.  Not both.
Sausages with gravey/jus/casseroled - mustard.
Sausages in no sauce - brown, ketchup or mustard.
Sandwiches.
Chicken - Mayo, chilli.
Beef and patties- ketchup, mustard, horseradish
Lamb - if you *must* have a lamb sandwich/lamb burger.  Minted mayo.
Pork - mustard, ketchup, mayo, chilli.
Corned beef - brown sauce, ketchup.
Brown sauce is not for main dishes. Ever.
Ketchup and mayo never goes on anything with gravy/jus/casserole.
mint is for lamb and mohitos
These are the rules, and any deviation makes you a pervert.
Slightly related.  I made Cornish pasties yesterday.  My wife put brown sauce with it ffs.  Ketchup/mustard.