Plastics are probably the largest semi-direct user of hydrocarbons other than energy production, and according to the US Energy Information Administration [1] plastics used the equivalent of 2.7% of the total oil consumption in the US in 2010.

If we just stop burning the stuff we'll have enough for other uses for a very very long time.

We can synthetize all petroleum products from carbon feedstocks, so long as we can pay the energy cost. This is generally true of almost everything these days -- all resources that the modern economy depends on are substitutable or synthetizable with energy.