Get an autism and inattentive ADHD test.

to do lists/ checklists with visual cues and consistent order.

Use visual cues. Print off some pictures and make some simple prompt posters. E.g Getting ready for school.
Use simple words to cue him in such as First, Next, Then. with a picture next to each word.

Having some visual reminders may help. Like a picture checklist of things he needs to do to get ready for school, and as he does them he can tick it off with a whiteboard marker or similar. Then have one the same for after school or getting ready for bed. This is something an occupational therapist suggested for my Miss 7, because she’s easily distracted and doesn’t have a great working memory due to ADHD. She’s incredibly gifted academically, top of her class for math, English and art, but struggles to remember what needs to get done to get to school. But she’s getting better with age.

My son is very similar. I got him to write a little list of all the things he needs to do in the morning before school (brush teeth, make bed, sunscreen etc) and another for after school (unpack lunch bag, clothes in wash etc.).
We just started it a week ago and so far so good. He sticks it on his desk which he finds easier to see and remind himself of the simple, everyday tasks.

My son is very similar. I got him to write a little list of all the things he needs to do in the morning before school (brush teeth, make bed, sunscreen etc) and another for after school (unpack lunch bag, clothes in wash etc.).
We just started it a week ago and so far so good. He sticks it on his desk which he finds easier to see and remind himself of the simple, everyday tasks.

Repetition. You may find yourself on repeat for years. For kids, things of interest will take over things they don’t have interest in. I would also consider seeing a GP to discuss possible autism spectrum (aspergers) and seek assistance.

Occupational Therapists can help with executive functioning tasks. Talk to your GP about a referral.

First, he’s only six. Some of these sorts of failures are pretty normal for his age. You can try things like charts or lists of things he needs to take to school/bring home. And if he has a watch already then set alarms on it with some reminders. But honestly, I think persistence and a few years might be the critical things here.

Let him do all of that, we learn by making mistakes, let him put his shoes on the wrong feet, it won’t take long for him to realise, same with his shirt (they sit differently on the neck.

Put a note in his lunchbox to put it in his bag when he’s finished eating.
Use a laundry marker to mark the inside of his shoes with a picture or word that reads/looks the right way when the shoes are together to go on the right feet.
Put a B on the tags of his shirts, for Back.

And, don’t stress so much. He’s 6. The world is big and full of far more interesting things than shoes, shirts and lunchboxes for him.

I have children like this too, some days I feel like a broken record.
Charts and lists that you can tick off and refer back to are great – eg a morning chart and afternoon chart to remind kids what they need to do each day.
Simple instructions just one thing thing at a time, don’t load them up with 3 things to do in the one sentence.
As an aside, have you considered psychometric testing? My child tested gifted but his visual spatial hit the ceiling. Have a bit of a google about Visual Spatial kids – there’s heaps of useful info out there and when you read it all, its a bit of an a ha moment.
A great book is

This is where we all need a Cricut machine to put labels on everything for constant reminders. Like a social story to create a lightbulb moment.

My 6yo is exactly the same. He is super smart academically but very forgetful and will often do his buttons up wrong etc.. I figure because he’s learning so fast and taking in so much information at once – something has to give lol and its usually the basics because that’s not what he’s concentrating on at the time. I just make sure everything is labelled really well and I double check things before and after he goes anywhere. I figure he’ll grow out of it eventually and just try and focus on how incredible he is in other ways.

I leave little reminders in the bedroom, on the wall in the kitchen, in the school bags and in the lunchboxes

This is so my six year old boy!
If he lacks interest it doesn’t even hit his radar!
His dad is also a genius and I’m often commenting that they have no idea about the simple things in the real world! My husband even forgot to bring his lunch bag home yesterday (but can dress himself correctly).
For the longest time when my boy was around 4 years EVERYTHING had to relate back to math and I do mean EVERYTHING or else he wouldn’t understand or do anything. All we can do is ride it out and hope it improves… a little

Heehee he’s pretty bad! I’m a Primary Teacher so I’ve met many absent minded kids, but he’s up there with the best! His sister is TOTALLY his opposite! Kindy tried to work on this as well (awareness of surroundings, memory tasks for low interest areas), but I fear they had no success. He’s very loveable though ????

Interesting. I’m still working on the lunchbox with teenagers! It sounds quite normal to me for a 6 year old to be like this. Maybe your child’s advanced ability in academic areas makes you think they should be of similar standard all round? As for how to remind them, I think making it something they want to do helps, so maybe there is a natural negative consequence when they don’t do something right (instead of just finding another bag/lunchbox etc.). Or maybe get your child to solve the problem. They might like making a labelling system, or write up some grown-up list they have to read and check to draw on their academic ability.