Instead of soap you can use a number of other products that have been
used to make natural body scrubs or face masks - wheat (or any cereal)
husk, tomato juice + pulp, fresh non-pasteurized milk, corn, clay,
apple peal/juice, etc...

We used to make 1-2 liters of fruit and vegetable juice a week to drink
and I used the pulp for this(or stored in the fridge). It's a nice skin
treatment and it's fun experimenting.

The trick is though that after spreading it on your entire body you
have to wait 10-15 mins for it to dry, (which makes it less comfortable
in the winter) then scrub it off with a sponge or plastic scrub...