Going through your bank statement line by line isn't anyone's idea of a good evening. I'd still recommend doing it, maybe once a year. It takes about twenty minutes and most people find something they'd forgotten about.
Normally it's a subscription. Something you signed up to on a free trial and never cancelled, or something that went up in price without you noticing.
On their own they're not much. £7.99 here, £12 there. You don't really feel it.
Add a few together though and it can easily be £30 or £40 a month. That's £360 to £480 a year. Over 25 years, before any interest or growth, you're looking at somewhere between £9,000 and £12,000.
So who's paying for it? Mostly it's you, later on. Future you might well have wanted that money for something better.
I'm not saying cancel everything. If you use it and you like it, keep it, that's what money's for. It's the ones you've forgotten about that are the problem.
What I'd suggest is simple enough. Pick an evening, get the last three months of statements up, and go through them. Anything you don't recognise or don't use, cancel there and then. Don't leave it till tomorrow because you won't do it.
Broadband and mobile contracts are worth checking too. When the deal ends the price often goes up, and unless you look you won't necessarily know.
It's not going to change your life. It might pay for a weekend away, which isn't nothing.