DD is in reception now, she started with:
2 jumpers
2 joggers (reception uniform at her school)
3 polo shirts
1 PE tshirt
1 PE shorts.
Using the school's 2nd hand uniform sales (run by PSA, 50p an item) I then got 2 more polo shirts and 2 more jumpers, plus 2 summer dresses and 2 cardigans as and when I saw them.
Also, I bought her uniform last July, between buying it and starting school she'd grown 3 inches (!) so I had to return it all and buy the next size up. So consider whether your DC is likely to do the same!
Label clothes well, and multiple times (I do on hem and on label(s) usually,with iron on labels/permanent biro). Label shoes, bags, coats, hats etc etc - I found the Easy2name funky shoe labels excellent, DD's have outlasted her actual shoes!
DD has FSM so school dinners every day. You can normally tell what was for lunch just by looking at her clothes... :o
Get something (keyring, tag etc) to attach to the bookbag, DD puts hers in a box with all the others from her class, finding them is a bit interesting at the end of the day, especially now they're practising for year 1 and doing it themselves (no afternoon TA in year 1 here).
Get them to practise putting uniform on & taking it off. Make sure that they know when changing for PE NOT to remove pants and socks :o apparently there were a fair few naked ones in DD's class the first couple of weeks of trying. Also check when they need PE kit from - our reception doesn't starting changing till after Easter as their uniform is joggers anyway. Try not to send them in tights on PE days, they're tricky to change.
Practise carrying a tray with some food on and keeping it level if they're having school dinners.