Reading, Writing, Arithmetic as standard and to a competent level.
For those who may not have the advantages of others: please, thank you, how to walk along a pavement in a civilised fashion, to smile and say good morning, to be helpful, to work hard, to be presentable, to be kind, to think of others, the dangers of illegal substances, the fact that there can be a decent life for them if they are prepared to engage with society.
For the academically clever: three sciences, French, Spanish, Latin, Mandarin, etc.
For the non academic: more practical things and possibly things that reinforce marketable administration and practical skills with a greater emphasis on vocational training that is not provided at the expense of the basics.
For all - and my son's academic school has done this - touch typing which is a godsend in our academic world. Far more helpful than all the design and technology in the world.
Optional subjects IMO should be: PE, art, design and technology, music, etc.. I would love to see more emphasis on things that require academic rigour. I find it very sad that my daughter at a comprehensive (from which we have now moved her) spent hours on what I would call the "hobby" subjects yet the mathematics teaching for her class (top set) was so poor I had to engage a private tutor.