I know this isn't direct the answer to your question, but watch your inventory levels and time your purchases with AGO sales.
Make note of how much product it takes to do one car (i.e. Iron-x, Wheel Cleaner, etc...).
Compounds, Polishes and waxes will last a long time because you needn't use a lot of product per vehicle. (I'm paying the price for overstocking, and I have too much of this type of product presently).
The opposite can be said of things like:
APC's,
Iron-X
Clay Lube (I use Megs D114)
Wheel Cleaners,
Tarminator,
Glass Cleaners,
Trim detailers,
engine degreasers,
hot-water extracting pre-treatment,
upholstery cleaner.
Micro Restore (cleaner for your MF towels)
DA Pads
Also, any drying agents or clay lube... which is why I rely heavily on a 5 Gal pre-mix (1:128) of Megs D114. It can be used for everything... I use it to clean up under the engine bay (after a full cleaning), door jams, trunk jams, drying agent and clay lube. I'll use it as a wipe down between polish and LSP steps. Yeah, it's that good!