My suggestions;
Medication. He can set a recurring reminder on his phone for 'send prescription request' and 'collect DC's prescription' every 28 days. As you can set an alarm to come on x hours/minutes beforehand, it could first ping at say, 9am after he's given the medication so he could send it straight away and then it pings again later in the day in case he forgot to do it the first time.
He could also make a tick box for when it's given each day and stick it on the cupboard door where the medication is kept or the fridge door and write the time it's given in there, together with a column/line saying Order Prescription and Collect Prescription on the appropriate day. That sort of thing can be knocked up in Excel in about five minutes and, more to the point, it's accessible to the DC as well, so as they get older, they can easily become more engaged and responsible for their own health - good for learning a lot of concepts around time, recording information, reading tables and the like, too - and they'll be able to say 'Dad, I haven't had my medicine yet' or 'We need to order my medicine now'. A Nanny or school staff would have to keep a record of any medicine given, so it's not particularly weird to do similar at home.
For snacks, just let it go. A snack of any kind is a snack and better than not having anything because he can't weigh up the variables and know you'd be OK with the decision.
Homework - he can add that in a routine,
SCHOOL PICK UP
Hang up coats/hats/scarves,
Shoes off,
SNACK and DRINK,
Check all bags
Take out things to be washed,
Empty lunchboxes & wash water bottles,
Take out any letters or homework,
Check on school website for any letters. Print and read letters,
Add tasks/dates with notes to a large calendar (so 'DC1 TRIP TO MUSEUM, school at 7.30am, needs packed lunch, pick up 4pm' on the 18th and 'PACKED LUNCH FOR TRIP' on the 17th),
Mark Letters with Done 15/5 for each thing added to the calendar
File letters for checking (not Newsletters For The Nanny).
Something else that can help is being aware of how he most easily absorbs information. He seems to glaze over after the first bundle of words, as does my DP although he sometimes glazes over as soon as he's asked the sodding question. Perhaps he finds visual cues easier? A lot of people find long explanations or huge blocks of text less than absorbing - keep it to the point. For a lot of people, using different colours and a lot of negative space works well, along with things like Sharpies, rather than standard biros for notes.
It helps bring a framework, logic and structure to things that aren't obviously structured - and he might actually quite enjoy finding order from chaos, as a sense of being in control makes it easier to accommodate changes, as when he understands his structure, he can then see how things fit together and logical places to insert extra tasks.
Essentially, it's breaking things down into small blocks of specific information/tasks, rather than 'do everything until I get home and tell you you've done it all wrong and forgotten at least five really important things in that stream of consciousness I subjected you to about three days ago'.
Yes, it sounds very regimented. It's not treating him like a child, though, it's him learning how to control and plan rather than have his mind pinging off in a thousand different directions at once, including trying to imagine what your response will be and letting half of it float straight back out of his mind again.