I am surprised the school hasn't told you? Didn't they send you info at the end of last term, or invite you to an info session? Is there some info on their website? Do you know anyone with a child at the school.
DD2 starts reception next week and having been through this with DD1, she will have:
Uniform on, school shoes on
Wellies (school has specifically asked for these)
School specific water bottle
Packed lunch (she is having that rather than school dinners)
PE kit in school PE draw string bag, although I haven't sorted out a PE t shirt (have to get it from the school in school colours) as I thought I still had DD1's but can't find it. But she is very very unlikely to have PE on day 1, or even the first week, so I'm getting that once school term starts
Empty school book bag
Absolutely no point sending in spare clothes in her school - if she has an accident (as DD1 did a few times when she started) the school have spare clothes (including knickers) and will put her in those. I am sure they don't check PE bags to see who has got spare clothes and who hasn't and they just use their stash.
If hot, in our school you send them in already with sun screen in. School don't apply it, and a 4 year old won't do it themselves, so no point sending that in either.