The answer to must of your questions is that it is up to you (not at all helpful I know) but the more you offer the more au pairs will consider you application and therefore in theory at least the more chance you will get a good one.
Mobile - we provide a phone with SIM and put a set amount of credit on it per month. Anything over that she pays for. This is mainly as I want her to be able to ring/text me or DH if she has issues or concerns. And amount others I know this is the usual thing to do. We don't allow her to call out on our landline (France) but she can have people call in.
Flights - no expectation at all! But we paid for our last ones flight home at the very end as a "thank you gift" next time though we think we will just give her the £100. If they fly home during their stay with you it is at their own cost I.e. for Xmas
Holiday - we give 4 weeks paid holiday and all bank holidays off. Again this is pretty normal. Last AP had a job interview so took an additional week unpaid but let us know far in advance and said she wouldn't go if it caused us problems. They normally go back for Xmas and then around (but not for) Easter.
Food - I have NO idea but not that much maybe £10 - £20 a week??
Language course - entirely optional, some don't want to do it. We pay £50 towards the cost of the course. Many give nothing at all towards it, some pay the whole lot.
Driving - cant tell you I am afraid. We don't allow any of our AP's to drive the children as their standard is not excellent and you need to be aware of the fact that though they say they can drive, it may not be as good as you would like.
There is nothing else you are expected to pay for but all household are different. Our AP's pay for their own shampoo, toothpaste etc as they often have brands they want. We will often give them lifts to college, into town etc. It all depends on the pocket money you pay as well. For AP outside of London £75 in minimum and for AP+ it is £85 minimum, but that is definitely a minimum guide and you will have to factor in how many children, how much housework, other jobs. Our AP only looks after children and the dogs (I.e. they are in the house with her, she doesn't walk them) no housework and she has a double bedroom, the next one will have the single bedroom so will be paid more to make up for that.
Bear in mind your AP has to be happy with their "package" as otherwise they can be disinterested in the children, sullen, unmotivated and eventually will leave but also don't fall into the trap that the more I pay the better AP I will get, as this is not always the case. Very careful selection and interview procedure are required.
I always think "would I have been willing to do that for the package AP is on when I was that age" if you are unsure then you probably shouldn't ask them to do it.
Sorry for the long reply, I hope it helps. Another questions feel free to ask.