The pool store sells a 'closing kit', which is the same as an 'opening kit'. It has oxidizer, stain and scale preventer and algaecide. I didn't use one when I closed this year, though I have the past two years. Do I really need this kit? I did shock the pool the night before I closed. I'm not quite sure what 'oxidizer' does? Wouldn't my chlorine shock have done the same thing?
Closing for me involves dropping the water level below the lowest line (in my case the suction line for the pool cleaner), blowing and capping all the lines, draining heater, pump, filter, etc etc. and finally putting a safety cover on the pool. Usually, we have enough snow/rain between now and April to fill the pool over the top of the skimmer.