When giving somebody a gift, consider the logistics the other person will face in handling it. This is true whether you're giving a kid a puppy (are you sure it will be cared for?), a spouse a surprise vacation (can we just pick up and go now?), or, in your case, a date some fresh flowers.
Fresh flowers need to be put in a vase or similar container with water. Other kinds of flowers (dried arrangement, potted plant, whatever) still need to be put somewhere so that neither of you is carrying them around as you go out to dinner and a movie. To satisfy these constraints, you give the flowers to your date at her house when you arrive, and you wait for her to put them in a vase. (If you have any reason to believe she might not have a suitable receptacle, you should consider other options.) This means you need to go to her house, not meet her somewhere else and not sit out in your car and honk your horn to let her know you're ready.
We can't tell you what gift might be appropriate, especially since you haven't said where you are. I'm answering based on both past experience with receiving flowers (in the US) and a broader gift protocol that says a gift should not impose difficulties on someone you're hoping to please.