Combining a conference with a personal vacation I received a funding offer from a conference overseas (as a PhD student), which includes accommodation and travel. I was wondering whether it is ethical to combine this business trip with a personal vacation? That is, to arrive e.g. a week or two before the conference (and of course pay for lodging in this "personal segment" from my own funds) and just get to know the country where the conference is held? Is it acceptable to email the organizers asking whether I'm permitted to come early? (This is needed to make sure that the airfare for such an early arrival is still reimbursable.)

I understand that this can be treated as an abuse of the conference's money, but on the other hand, it does not make any financial difference if I come earlier (however, see the remark below). And I'm still going to keep attending the conference as my main purpose. Moreover, coming earlier may result in purchasing a cheaper plane ticket (around 200 USD cheaper), in which case the conference's funds will only benefit.
Yes, it is typical to take personal time before or after a conference. Funding from your university would not usually mind.

Conference funds may be a little less flexible, so you should certainly check with them. With evidence in hand it will be cheaper for them, I find it unlikely they would decline.