In an effort to minimize effort
we used what was handy--(usually unpainted) plastic Airfix/ESCI/Atlantic/etc figures, ROCO Minitanks and/or Matchbox/HotWheels vehicles, any pre-made buildings we had handy (HO Plasticville) or just carcboard boxes of the appropriate size and shape. The 20mm scale was handy enough to allow detail and yet be of manageable size. The occasional 6-sided dice were used to round out incidental potentially mobile items. I purchased a sheet of heavy plastic sheeting to use grease pencils on to designate streets, buildings, fire hydrants, streetlights, mailboxes....
To allow for a fog-of-war factor, to designate "bogies" we would use poker chips with the actual identity of the unit/vehicle/object taped to the underside. Only coming within a certain range would allow identification of the chip's identity