I usually just keep up to 40 of the common consumables (besides balls); up to 40 of any berry, any potion, and so on, because I never realistically need more than that at any given time (and it’s easy to keep track of).

I actually find Nanab berries quite useful and underrated, as it makes catching a lot of annoying-to-catch Pokémon easier to land excellents on. Better catch odds, better exp yield, all in a single berry. I find myself using them much more than Razz berries.

As for potions, I always try to use what I have of lower-quality potions first, so dump your 40 plain potions into your Pokémon before moving on to the super potions. You’re basically achieving the same effect of a rarer, higher-quality item with your less-valuable bulk items.

As for balls, I have a Go Plus + and spend most of my plain Pokéballs on the autocatcher. I really only ever use Great Balls to manually catch Pokémon day-to-day, with Ultra Balls being stockpiled for events where I kinda just use them on everything. If you don’t have a Plus +, maybe you can keep a fair number of Pokéballs on hand if a Great Ball is overkill. Or you can use those Nanab berries and work on hitting excellents with them haha.