You know, I started trying to streamline my arsenal a while back. This is what I have decided on making the "core" of my arsenal:
ONR:
Clay lube
Interior Wipedowns
Door Jams
Quick Detailer
Use it to remove polishes when they are "sticky"
Car Washes
I have a gallon of QEW (prefer it to ONR for washes)
I have a gallon of DuraGloss for regular washes
Glass
Zep cleaner from Home Depot - 1 gallon makes a bazillion when diluted
Engines, Wheel wells and Undercarriages
Any APC that is on sale, diluted to required strength
Dressings
Optimum Protectant Plus for leather, dash, and other interior surfaces.
Meguiar's Hyper Dressing diluted for engines, wheel wells, tires, etc
I will also keep a tire gel (one that's on sale) on hand for when more durability is needed.
Waxes/Sealants
Zaino, DuraGloss and FK1000 - sealants
CMW, Collinite,
M26, and Sauveran - waxes
Polishes
M105
M205
M86
3M ECC
3M UF
SIP
106FF
Menz
Final Polish
I can accomplish most everything needed with the chemicals listed above. I will probably have a fire sale soon in the classifieds.