Agree about the detentions - I've taught pupils who've been so anxious about getting one, and the longer it goes on without one, the more anxious they get. Once it's happened and they know what it's like, they relax and feel much better about everything. it doesn't mean they don't care or don't try not to get one, but the fear of the unknown is removed.
Cards, keys etc on a springy lanyard in a bag can be useful, if they always have that bag with them. A sneaky fiver or a few coins somewhere that they don't use often as an emergency is handy, if you can trust them not to just spend them every break!
Spare pens and pencils that you don't mind getting lost, so that they can on occasion lend them out to someone who doesn't have one, which can be a useful way of starting to chat to someone.
Photo of timetable on phone.
Write down clearly all the user names and passwords for every different email, homework site, maths program etc etc. So many children put them in once, have the device save the password, and then can't remember it a couple of months later when they have to log in somewhere else, or reset their device or whatever. Then they can't remember to go to the IT office or teacher to get a new one, etc, and there's no access for ages to their accounts.
Sorting out any extra loose worksheets, tests etc and keeping them somewhere safe, preferably in the book or in a pocket attached to the book. Encourage children to bring home the whole book if they're allowed, rather than just the one page of homework that they think will be easier to carry, as it doesn't end up getting back to the right place, and then when it's time for a test, all you have are half empty books, and random screwed up bits of paper at the bottom of a bag or shoved in other books, or even notes at the back of other books. They don't always encourage a jotter book any more, but you could provide a small notebook if they don't, for times when they do need a bit of paper to write something down, so that the useful information doesn't then end up scattered at the back of whichever exercise books are handy at the time.
Learning to use the reminders app on a phone can be handy, depending on the school policy on phone use. You can even be really specific and get it to remind you of something once you physically enter the school grounds, for example, as well as at whatever time. You can make it stay on the front screen of the phone until you click 'done', so that it's always there reminding you even if you don't do it straight away. Or get into the habit of resetting the time on it, if you don't do it straight away. Useful for reminding them for anything, like 'tell mum about food tech ingredients when I get home' or 'turn in permission slip for school trip at the office instead of carrying it around all day' or 'remember to go to maths tutor'. The more they get used to using that (or a paper diary and remembering to check it), the more they can put in it.