When I was at school I considered the below a waste of time and would rather have spent the time studying for subjects I wanted to pursue:
-Music
-Art
-Some of the PE / Games lessons (I recognise the importance of physical activity, but ideally children would be able to focus more on the activities that interested them. I don't really see how gymnastics for example where half the time was stood around waiting for your turn on the equipment was essential learning once you'd tried it a few times)
-2nd foreign language (no issue with people doing this out of choice, but it's not really helped me much at all since finishing GCSEs 25 years ago)
Music and Art were especially annoying because I didn't get any qualifications from them and yet still had to keep studying them for years into secondary school, absolute nonsense being the age of 14 and being forced to waste time on stuff you've known for years you have no interest in and are not taking for GCSE.
Of the subjects I did take at GCSE I'd say the languages were the biggest waste, 5 and 4 years of study respectively and have been barely used, if you think about it they are quite niche as when in England you speak English 99.999% of the time, and most people don't spend much time in countries speaking the languages you've learned, and with English being widely understood overseas anyway it's hardly essential.
More broadly I left school a little fed up at having to do 9 subjects at GCSE but only 3 at A-level, if felt like the balance was wrong to me, that meant I had to pick Spanish just to make up the numbers (wasn't interested in it really) at GCSE and yet at A-level you can't continue studies in things you enjoy, I had to ditch History despite being interested in it and pretty good at it. Would much rather have seen an 8/4 split, I also found GCSEs a really heavy workload due to having so many subjects and no free periods, whereas A-levels was a bit of a breeze with only 3 subjects and free periods where you could study etc.
Things like Maths, English, History, Geography I use on a regular basis, Home Studies or whatever it was that taught some finance stuff was vaguely useful, IT was a joke at my school but again I use IT stuff a lot, CDT whilst I don't use that often again at least taught a few practical skills, on the science side I'd say Physics is the most useful but there's bits and pieces from Biology that help, RE did teach me about different religions etc I had no idea what all these things like Hindu/Sikh/Buddhism etc were until I went to secondary school.