What should never be missing in a pie?

The first two photos are steak and ale pie, and the third one is potato and steak pie.

Some time ago I made a potato and steak pie with peas, and a few days later I made a steak and ale pie with peas and mash. In both cases I made my own pastry, because on Come Dine With Me they always shame people for not making their own pastry.

My husband is British and he loves pie, but we live in Peru where you can’t buy them anywhere. So I’ve decided to cook them more often so he doesn’t get nostalgic (even though he’s already been here for 10 years).

I’ve seen a lot of recipes, each with small variations, but I’d like to know: what are the things that should NEVER be missing in a pie?

Luckily I have Oxo and Bisto gravy (beef, chicken, and vegetable). I’ve run out of Henderson’s Relish, but I can get Lea & Perrins here. I also have malt vinegar. For mash, I try to pick the whitest potatoes I can find at the market, and for the peas—well, peas are peas.

Thanks for your advices!