What do you Brits put on yours?

I prefer to start with a bit of butter (not margerine), followed with a copious amount of sour cream, ground black pepper, garlic salt and if available chives.
How about you.

Butter (lots and lots) and salt, mostly. Sometimes cheese and bacon.

Ages ago in the UK, I had a really nice one with baked beans on it.

Half a ton of butter, salt & pepper and cheese. Lots and lots of cheese.

Tinned tuna and mayo, preferably with some spring onions or celery for a bit of crunch.

Butter, sour cream, butter, cheese, butter, chives/spring onions, and, er, butter. Sometimes bacon, but that really isn't necessary.

The typical stuff you find at sweet tomatoes

Coastal brand cheddar cheese.

Tuna, mayo, corn.

Or curry.

Or any left overs...bacon is always good.

Cheese and coleslaw, Heinz baked beans and cheese, leftover chicken tikka masala, tuna salad, or do twice baked potatoes with strong UK cheddar, bacon and spring onions (think you call them salad onions)

On a jacket potato my favourite is grated extra sharp chedder. No butter needed if there's enough good quality cheese...IMO of course.

As an alternative, I'd also consider a nice tuna mayo corn topping. And spring onions are a decent addition no matter what else there is.

I vaguely remember something called potato toppers, or was that just toast toppers in the UK

Tuna mayo, which includes sweetcorn and chopped spring onions.

Home-made chili.

Mostly (because it's easy and quick) butter, then a handful each of grated cheese (strongest cheddar-a-like I can find), spring onions and sweetcorn.

When I was a student, way back when in the Midlands, baked potatoes were a standard takeaway food from little vans - the default there was butter, baked beans and cheese, as it was the best price/ calories ratio.

I've only heard the term "baked potato toppers" here in the USA. And usually they include some kind of sour cream. Not my favourite, sour cream on potato....

IMO, the toppings in the UK are more like fillings than toppings... thus more like a meal with a jacket potato base. American potato toppings seem more like a side dish, rich maybe but not a main meal.

pretty much anything lurking in the fridge!

Lashings of Kerrygold butter so it oozes under the potato and gets on the skin as well, and the potato can't touch anything else.