First thing, Don't panic! In most cases the kidnapper is just as scared as you are. If he or she already has you in the car don't continue to scream, That will only make the kidnapper more nervous.
Talk to the kidnapper, and keep your eyes and ears open. Watch street signs and look for identifying marks on the kidnapper. Listen for anything important he or she might say. Try if possible to get personal with the kidnapper.
Tell the kidnapper stuff about yourself it's harder to hurt someone you know. If the kidnapper wants sex don't fight it, it's a terrible thing but it won't last that long and it would be much better to walk away from the situation then to not.
Do and say whatever you have to, to make the kidnapper feel like you genuinely like them so they'll feel safe enough to let you go without you telling on them.
As soon as your dropped off by the kidnapper get to the nearest phone and call the police!