Traveling with wine

[EY]

I am planning a trip to CA where I will visit Napa Valley. I imagine I'll buy at least a few bottles of wine and was planning on taking them on the plane with me. However, I will be traveling with the wine in a car for a day trip and was planning on leaving the wine in the car while I did the tourist thing for the day. Will this harm the wine or am I OK? Any tips on keeping the wine from spoiling are also appreciated.