For some things but rust will really destroy a lot of the valuable metals like iron as it decays then scatters, a lot of how useful that will stay will depend on how long and deep the collapse is. One of the main things will be energy as so much of the surface coal and easily accessible oil have been exploited. The best bet is probably recovering and refurbishing electric motors to rig generators but there's a lot of infrastructure around turning that into reliable power that would also be tough to recover.