how to look after themselves on a basic level - i.e. basic cooking, how to operate a washing machine / iron / dishwasher etc, how to clean a toilet and how often you should do it.
money management - the concept of budgeting, saving up for things and responsible use of debt (and how interest rates work)
the fact that the world does not owe you a living, if you want one you should get off your bum and make one.
that you should be grateful for what you do have, not bitter about the things you don't have, and generous to those who have less than you.
basic contraception, including not getting so incredibly drunk that you "forget" about using it.
how to do basic DIY and car maintenance
how to consider other's motivations and points of view in a professional sense, e.g. what is the person holding the interview looking for? And how can you best present yourself given this understanding? This last one is sadly lacking in most of the candidates I interview, and is a skill gap that is felt in the workplace too (e.g. when negotiating in meetings).
that different people can have vastly different opinions and that's ok, you don't have to agree and you don't even have to like everyone or be liked by everyone.
be true to yourself and you'll never do anything you regret!