It may be the way a girl says 'Thank you' to the boy for giving her a good time. It may signify their special awareness of each other as dating boy and girl friends. Or it may be a very special token of genuine affection. What it means depends upon the two persons and their definition of their relationship and of themselves. Most girls, and boys too, agree that the first date is too soon for a goodnight kiss.
Girls say that it seems too easy when it closes the very first date.
Boys sometimes confess that they will try to kiss a girl the first time they take her out but that they really do not expect her to allow it, especially if she is the kind of girl they respect. Both boys and girls generally feel that a couple should have seen each other long enough to have become somewhat better acquainted than is possible after just one date, before they kiss each other. This is a good question, but hard to answer precisely. It depends upon the persons involved, how they feel about each other, how well they know each other, and what kissing means to them. Some couples date for a long while and never are particularly interested in kissing.