Like
DHR-107 and
BladePrincess, I have a nice sized medical bag any time I can. I sort of have a system:
Healing Items:
1. Early game have at least one Potion per Pokemon, two if I can afford it.
2. When Super Potion becomes available & its before a vending machine, same as above.
3. By then I find a vending machine and I might as well just unplug the vending machine and carry around in my backpack. By then I have plenty of money so I buy 18 Water, 18 Soda Pop, and 18 Lemonades (3 each for my Pokemon). (BTW, GF, please let us buy this stuff in bulk. I know that's not real life but can we just assume my trainer picked the same choice multiple times instead of me actually doing it?)
4. Same once I get access to Moo Moo Milk.
5. Before Elite Four/Champion I buy 50 Full Restores because I can.
Curing Items:
1. When curatives become available I buy 3 Antidotes, 3 Paralyze Heals, and 3 Awakenings (if there is like a Fire-type Gym before Full Heals become available I may buy 3 of them before the Gym, however I usually skip on Burn Heals and Ice Heal since by the time you encounter these types you usually have access to Full Heal).
2. One Full Heals are available I buy 10 at a time, usually selling any other curative I have.
3. Before Elite Four/Champion I buy 50 Full Restores because I can.
Revives:
When I can finally afford it I try having a revive or two for each of my Pokemon. I buy like one extra for each before challenging the Elite Four.
Berries:
I never use Berries as I'm too lazy to plant them and remember where I plant them... except in XY. The Berry Fields was SO convenient, especially after getting Fly, I eventually was able to stop refreshing my supplies if I used them. PLEASE GF, bring back XY's version of the Berry Field and not that circular travesty you called a Berry Field in ORAS.
Ethers:
I never use them though never sell them, I just hoard them. Maybe I may use them in a pinch, but if I come to the end of the game I usually sell them as at that point I don't need them anymore. That said I still kind of wish GF made them available in some way, even if an item from marts (though they'd have to make them cheap enough to be worth it).
Though for games before Gen VI this was easy to do since you got nothing to spend your money on. But now that we have customization I find myself early game forcing myself to not buy any new clothes as I need money for healing items and then once I have enough I sparsely buy clothes. I'm just hoping they include the Amulet Coin and a money grinding spot in an early location like they did in XY (thinking about it several parts of XY had good planning design like the Berry Field and the money grinding location, both located on Route 7 which isn't that far deep into the game as you may think).