Other countries expect their pupils to buy their own supplies, books included. I don't understand why parents don't buy their kids books and expect everything to be paid for frankly. (maybe some schools do, but so far my own kids haven't had to pay for anything here).
I don't think schools are unreasonable at all to ask when there's not enough budget to cover enough TA and teachers are begging for pens and paper. It's not fair everything has to come out of their own pockets.
I am truly sorry some parents struggle with day and residential trips, but I do see them as essential. It's not fair to expect kids to be stuck in a classroom all year round, they already have such short summer holiday here (many posters already have their kids home).
Schools are trying to involve parents and make things interesting. If you can't make a concert, just don't go. I am trying to make most of them, can't say it's the highlight of my year or even my week, but the kids are proud and I love that they are shown of the various things they can do, not just basic "studies" in the classroom.
As above, financially things will only get worst, look at the budget cut predicted by 2019.