I have stored enough soap for many years use,it is cheap and appears to keep indefinatly.
Liquid detergent as used for diswashing can also be used in the shower, but is rather drying for daily use.

I keep 25 litres of diswashing deteregent, which is enough for several years use.
I keep at least 100 bars of soap as used in the shower, one bar lasts at least 2 weeks.
For laundry I keep about a years worth of detergent.

In normal conditions I shower daily, but only with plain hot water.
I use soap or shower gell only if engine oil, paint, soot ect requires removal.