I imagine those 'mcMansions' going the way of some of those neighbourhoods in Detroit: just the odd lonely house standing amidst deserted lots with rubble in them-- maybe with huge razor wire fences on the survivors (South Africa is a bit like this in places).  Homeless people sheltering in the ones that remain.

Some people in the society will always have access to fuel and transport.  They will cluster in protected zones or parts of cities.

Plastic is harder to recycle.  Burning it strikes me as the height of folly-- what if your kids get a whiff?

After D-Day, the Germans (a garrison of about 8,000) were dug in Jersey (British island off the French coast) until V-E Day.  The local population (about 20,000) nearly starved as all supplies were cut off.  Eventually a Red Cross Convoy was organised from England to provide some food to the locals.

Same thing happened in Holland from September 1944 to May 1945.  The Dutch had assisted the Allied paratroopers, and the German occupation authorities simply cut off all food and fuel transport, through one of the coldest winters of the Century.

If someone wasn't living in their house, the roof and furnishings were stripped for firewood, ditto the trees.

This is why up until modern times there were severe penalties for cutting down trees on private or common land: down to losing a hand, whipping or permanent scaring.  Primitive societies have always had social means to control deforestation.