If you search there will be a few really long threads on this.
Good tips I got (DD now yr1) is the name everything -gloves, pots they take fruit in, shoes, pumps - the lot. You can get sticky labels that survive the dishwasher.
If you have a day out buy a few of those personalised keyrings in the gift shop for reading folder, pe bag, coat zip etc. Much easier for child to spot in a pile of identical bags.
Do check they can eat their packed lunch - if they always have food on a plate suddenly having things wrapped in clingfilm is hard. I personally use little pots for DD as she finds it easier (those tomee tippee weaning pots about the size of a yoghurt pot) so a pot of grapes, pot of cucumber.
Make sure you get all info you need before the school shuts for summer - uniform list, do they need fruit for a snack etc.
Do not leave uniform buying late especially if it has to come from school/authorised stockist.
If possible maybe go to any school events eg sports day, school fair so it is all a bit less stange for you both.
Don't stress if he can't fully dress/fold his clothes etc - that is what they practice in reception. I was so worried about DD as she has a disability (born without left arm). At first parents evening I was asking her teacher - and she reassured me DD was the best in the class - lots just stood there waiting to be dressed.
We also read a few starting school books - topsy and tim etc