An all-shared system and an all-separated system both break down in different ways
If everything is centralized, people can lose access to the medicine that really must stay with them during stops or split movement.
If everything is fully separated, groups often waste time searching multiple bags for the same small urgent item.
High-frequency small items are usually better when centralized
Plasters, wipes, disinfecting pads, motion-sickness aids and simple stomach basics are often the things people need suddenly and repeatedly.
Keeping them in one clear car kit reduces stop-by-stop chaos and lowers retrieval friction for the whole group.
Personal essential medicine must stay with the traveller, not with the cabin system
Prescription medicine, scheduled medication, allergy-specific medicine and child-specific essential items should travel with the person who depends on them.
The key issue here is not tidiness but separation risk.
The strongest setup usually combines one shared layer with personal reserves
A small shared basics kit plus personal must-have medication creates both order and access security.
That is usually more reliable than trying to solve every need with one storage rule.