Try to get a lunch box with a shoulder strap as well as a handle and one that he can put a water bottle into easily - at our school, they have book bags that are more like music cases and just have a handle, plus a water bottle, plus a coat or jumper or bit of artwork etc etc and of course dc wants to hold hands and you end up needing hundreds of hands.
I've also got myself a dedicated reusable shopping bag from one of the supermarkets (one of those jute ones that go over your shoulders that I can use to stick in everything that needs to go to school - I have one for each dc. Then I can thrown in snack, water bottle, book bag, lunch bag, games kit if it needs to go back in, ditto wellies or coat etc etc. I also keep a few envelopes and a biro in there so if I'm running late in the morning I can sort out lunch money or whatever once we're at school. Means that there is a dedicated place once we are at home for all the school stuff to be, there is only one bag to pick up to go into the car in the morning and everything in one bag to bring home and then have hands free to hold dc's hand (see above).
Tesco make some good photo keyrings (The square or rectangular plastic ones are the ones I mean) that are like credit cards - so you can stick a picture on it of something they want - and if they are particularly attached to a favourite toy that you don't want to risk going into school but still want them to have some comfort from, then take a close-up picture of favourite toy and then turn that into the photo keyring. Then dc will still have favourite toy sort of with them in school but you don't have to worry about the actual toy being there, getting lost or damaged etc and also nobody else is likely to have the same keyring.
Get yourself several clothes marking pens and leave in useful places as you always find yourself with unmarked stuff that needs to go in despite having done the whole lot of your kit beforehand. I have one upstairs on my landing window (near the airing cupboard and where I put out the dc's clothes the night before, and near where they get dressed in the morning), one downstairs and one in the car. Ditto a black sharpie for labelling non-clothes gubbins that needs to go in. Then if names have faded or they are wearing mufti or whatever, you can just label as you need to.
Get used to getting everything out the night before that needs to go - uniform, bags etc assembled by the door, shoes ready, coat if needed... And whilst it might not be possible to get a lunch box ready the night before, see if there are any bits that you can do - make sure you've got enough clean little boxes, any biscuits/crisps/whole fruit/etc that doesn't hurt being in the lunch box overnight put there, anything that can be done in advance (ds used to like to have a pot of grated cheese so I'd do that and leave in the fridge, ditto a bag of chopped cucumber and pepper, plus he liked crackers so I'd put them in a little box in his lunch box waiting) and have water bottles there and ready to fill in the morning.
Mornings are always really hectic - anything you can do to streamline them for yourself will make them less stressful! And if your dc is finding it stressful to be getting ready and having to be out of the house at a certain time rather than at their own pace - then you want to be able to concentrate on them rather than finding yourself rushing around!