I'll answer your original question, Dilbert. Both of mine are at boarding school, neither have school uniform, so I can't help you with that one. The unofficial uniform appears to be T shirt, jeans and hoodie or thick tights, shorts and hoodie. Primark is worn as much as Abercrombie or other high end brands.
At DD1's school, the full boarding fees include all weekend outings and the ski trip at half term. We have had very few "extra" school trips, mostly being of the local variety, so £20 to go to some nature reserve around 20 miles away, and this includes the lunch out and coach there and back. There was one compulsory trip, an outward bound one, at the beginning of 9th grade, which cost around £400 for the week, including coach there and back, and all meals. Other trips this year, which are all optional, include Ypres, Moscow and Florence. They are entirely optional, about one third to one half of the kids will go, so no stigma attached if you don't go.
DD2's school does local day trips, which cost around £20, and a 3 day trip to Ypres, which was £135. All compulsory. There is also a language exchange next year - if the boarders go on this, the exchange child comes and spends a week in the boarding house with them. But it's not compulsory.
DD1's school fees are extortionate (think £40K plus for full boarding), but fortunately, as part of my expat package, I get a chunk of these paid for. I am quite sure we are the poorest family in the school, probably by quite a long stretch, but it seems to have made no difference to DD1's friends (they are all quite nerdy, like her).