hey
the room will come with a bed, wardrobe, desk, chair, a bin, shelves, a lamp, and that's about it. in the bathroom there'll be a mirror and usually a toilet brush, along with a shower (w/ shower curtain), a bin, and a toilet - so for the bedroom I'd recommend a doorstop (because the doors automatically shut and lock unless propped open, and in the first few days it's good so people can come in and talk to you), hangers for the wardrobe (because there are never any left), pins to put things on the cork board, bedding (obviously), and maybe something that could be a conversation starter? that one's not the most important, but a poster, toy, or a picture with a story behind it is quite a good way to make friends
for the bathroom, obviously shampoo and all that, a few towels, a mat to put on the floor so it doesn't get wet, and toilet roll because they don't provide that.
for the kitchen you'll need everything - plates, bowls, cutlery, dish cloths, washing up liquid, kitchen roll, bleach, sponges. with some things, split the cost or take turns in buying it so there aren't arguments
also, one thing I found useful is to bring something that other people might not have - something like Febreze - so people can go to you for help basically (not ideal for everyone, but it's nice to feel valued haha)