Black Friday is largely a retail con trick. See here:
https://www.bbc.co.uk/news/business-59380453
However there are still a few bargains to be found, even if linking them to Black Friday is a bit crafty. For example, Morrisons occasionally offer full breakfasts in their café at half price. As they happen to be doing do this week, they've called it a Black Friday promotion:
https://my.morrisons.com/blackfriday/
(Irrespective of whether it's really a Black Friday deal or not £2.97 for a big meal out is a decent price anyway!)
Morrisons are also selling bottles of Prosecco for just £4.49. They've labelled it as a Black Friday deal in their stores (but not, I see, on their website) even though the offer doesn't end until the 12th of December.
Amazon periodically drop the prices of their own products, such as the Kindle range. They almost invariably do so as part of a Black Friday promotion but that doesn't mean that you won't be able to find those products at the same low prices at certain other times of the year as well.