I've often wondered about this too.Reading Evgeni Bessanovs book Tank Rider gives some insight as to supply being almost non existant.He makes reference during the fighting for Kamenets Podolsk that ammunition actually ran out for PPSH and his men had to use German weapons.Also they lived on flour and water for an extended period.This was at a time when his battalion was down to 30 men with no heavy weapons.Perhaps this unit was so reduced as to be written off therefore intentionally not supplied ?
Bessanov also writes that food was'nt too much a problem in the Eastern Ukraine,where they were treated as liberators but once they advanced further west resentment towards Moscow,by the local population,meant that threats had to be used in order to gain food.