Plastic packaging made from virgin polymers are strong and re-useable, even for building structures, rather than heading for recycling centres.
Bags filled with small amount of water and tubes to support them can quench fire, thus forming safe structure, as long as wet weather conditions persists. However, some cups, food trays, tubes become fragile under prolonged UV exposure, few months of summer Sun would render them useless to support structure. Thus protect them with UV cover, such as wood, dismantled and cut from pallets would be essential for longevity. Over time, algae and moss would grow and capture carbon dioxide too.
Chemical waste in solid, liquid and gaseous forms are tricky to deal with. High temperatures and pressures from geological sites such as volcanic and fault-lines, may be accessible with planning, to dispose them safely.
Building materials from demolition may be processed by sea. At shores, bricks and stones will become round and smooth over time, due to tidal action of persistent grinding by pushing and pulling them with water waves. Reclaiming land from sea is possible too, as well as forming barriers to prevent coastal erosion.