But he has tons of downtime between cases, what we see in the books is only a few weeks out of every year for him. I dunno, it just doesn't make sense unless the potions have an expiry date or something. Even if he can do that stuff with his normal magic, it seems silly to drain energy he could use blowing stuff up, especially with veils and shit he's usually not good with, when he could just gulp down a potion instead. There's no reason he couldn't carry a flask or two on each leg, an invisibility potion, the escape/teleport one he did, the energy recharge one he used in Fool Moon, etc. He already puts so much time into building/rebuilding/maintaining his other equipment, seems like spending a day brewing up a couple of potions would make sense.
I mean I get that the reality is that it's a literary thing, authors always forget that these things exist until they think up an excuse to use them, just kind of hard to believe that they wouldn't be utilized more than we see them. Even if not Harry, you think the Wardens wouldn't carry a few potions on them as part of their standard battle getup?
Also, what happened to that belt buckle? At one stage he had a belt buckle shaped like a bear which he used to store a charge of energy to refresh him during battle, but he used it once (think it was the book where he's working on the porn set) then we never hear about it again.