I'm in the same boat, 30 (I still can't believe that) and no kids, not married and honestly not really interested in either of those. By the time my time is up my parents will be dead, naturally. I have a sister who has kids though, she's older than me, so for sake of this conversation let's say she's gone too. My nephews would be adults by then and settled with their own house/job etc, possibly married, so I imagine they'd take care of me/come see me (not that I plan to actually give them that burden) and I'd probably be in an old age home once I can't take care of myself. They'd probably end up with power of attorney at some point.
As far as inheritance, I actually need to make a will, I will probably put my parents, sister/brother in law, and nephews. So depending on when I die and who is alive it will be spread accordingly. The actual details I'll have to decide when I actually get the will done. I can get hit by a bus tomorrow or live to 100, so that changes things.
Idealy I want to skip the whole old age home thing and die suddenly from some really epic or hilarious accident and not be a burden on anyone. Or maybe some kind of heroic act where I die saving someone.