Hi Rosetti!

Are you booked into a hospital?

Do you have an IM?

If you are booked into hospital without an IM then I would call an ambulance. that time after birth is always a good time IMHO to be close to your care providers (in planned HBs your IMs generally stay at least a few hours PP to watch you and baby...temp taking, obs on you and baby etc...and of course they are on 24 hour call after that). Even if the birth goes really well I would in my own situation want to still be cared for by someone else in the birth know ITMS. So in that case, yes, i would call an ambulance. and i think nickle answered your question about if you have to go quite well in the event of an unattened and unplanned birth at home:

If you deliver unexpectedly at home and call an ambulance, I will expect that you wish to be transported to hospital.
If you are booked into hospital but also have an IM the situation might be different. if the IM is there, they might be able to assist you and look after you at home if that is what you wish. If you still want to go to hospital then she/he will also still go with you.

if there is concern or history for PPH then ambulance might be advised by your IM for transfer etc.

things on hand for unexpected delivery...not much just have some towels on the ready. the most important thing would be to keep baby warm. lots and lots of skin to skin and a beanie and keep that baby warm! i would turn on the heating if the weather is iffy temp wise.
if you BF, get onto it. it helps with the placenta and bleeding.

i have very fast births so even with a planned HB i still have my 'grab' bag JIC i were to go into labour with nobody to help. this included:

several towels.

bunny rugs/wraps

beanies

rescue remedy drops

and (because i may or may not be a dirty hippy lol) some arnica at 200cH to help with bruising/swelling/bleeding (it is taken immediately after birth).

I would recommend maybe thinking of a safe space if you are worried about a precipitous birth where you feel that you could birth feeling safe and easily accessible to the ambos etc...like for instance, somewhere near the front door if you are on your own and need to open up when they arrive...you could still be feeling quite shaky etc.

do you have neighbours that you could call upon in the interim between calling an ambulance and them arriving? someone that could help with kids/door opening etc? maybe have a key under a rock at the front door lol!