It really depends on the pool, local conditions, etc. Some people go through gallons of acid per week, others like myself probably have not used a gallon of acid in the last 5 years. (the truth is I have mostly switched back to dry acid because the muriatic acid bottles get brittle and fall apart after a couple of years).
As to what I personally keep on hand,: (keep in mind I have an indoor pool)
A few gallons of bleach (I have a metering pump connected to a 15 gallon drum which I refill) typical bleach use is about 1 quart per day
about 10-15 pounds of MPS (only used after big pool parties for supplemental oxidation)
a container or two of pH up and pH down from Lowes again my pH is very stable and rarely need adjustment and while I could use the grocery store options (borax, washing soda, etc.) I like the moisture proof screw top containers even if they do cost a little more.
I also keep some chlor out chlorine remover on hand, being an indoor pool it takes forever for FC to drop if something happens and I need to boost up to SLAM level, or remove chlorine to do an ascorbic acid stain treatment.
I also tend to keep about 10 pounds of granular CYA stalibizer on hand to tweak CYA when needed plus I have a tub of trichlor pucks, still 75% full and 6 years old, and a couple of cases of 1 pound bags of dichlor that I acquired for free a couple of years ago. This is all a bit redundant for various FC/CYA tweaks, but gives me flexibility.
It may sound like a lot to have on hand, but the nearest store that has year round pool supplies is 30 miles away (Lowe's) and sometimes they are out of this or that, and the second closest is 50 miles away in a different direction.
Ike
p.s. my pool has a vinyl liner so no CH increaser needed even though we have very soft water (50-60 ppm CH from well water depending on the season)