My dad would say it's "payment" for buying a meal.
Most Helpful Guy
It can be a lot of different reasons why someone do that.
Here you have a few.
1. He's testing where he has you.
2. If you kiss her on the first date you doesn't get in to the friendzone (funny assumption that are flying around)
3. He are after something more.
4. He have feelings.
and so on...
Ask yourself why would you do it!