Nothing.
I will be single for the rest of my life, there will never be children. I have no desire to ever get on a plane again, or for far-flung foreign travel. I have no interest in fashion, expensive watches, or preserving looks I never had. My savings are hopefully going to the beneficiaries of my will. So I refuse to define anything I do spend as being self-indulgent or extravagant. I try and buy decent quality products at a decent price & make them last. I have a hankering for a velomobile (or two) & a Moulton (or two) but unlikely ever to spend that money. Other people's children are welcome to shoes at my expense.