When I find automotive items on clearance I pick them up whether I need them now or not. I've found NXT carwash and window cleaner dirt cheap and bought enough for several years. I bought several cans of CD2 on clearance-and that is a tough product to find. I recently started picking up the Q Torque synthetic because it was as cheap as a conventional oil. I also hit the AZ Castrol special several times because that was 1/2 price.
I don't see the need for a 500 quart stash but when the economy is in the toilet sometimes you can find some great buys.