A will, which helps determine who gets what when you die.
A Lasting Power of Attorney, where you appoint trusted individual(s) to manage your financial and health & welfare affairs, if you can't do it yourself.
However, on their own, these measures can often not be enough. They provide only limited protection for your estate, both when you die and whilst you're still alive. Which is why we also recommend another key tool - A Family Asset Protection Trust.