[YouHearMe?]

First, I have to agree with Acheron; it's best to stay away from buying the girl(s) something as an opening to getting their attention. First, as he said, it's gonna look like buying affection. Second, if it turns out, like you said it might, that one girl rejects; any other girl who noticed will feel like second place should you offer one of them the bottle of water.

If your goal is attracting any random one of the girls, it seems like your best bet would be to carry on being outgoing and enjoyable.

If you have a specific one in your sights, I would go with making an emotional connection with her specifically, again- after getting her to take notice of you (simply so she has an idea who you are when you initiate contact).

Now; looking at your battle strategy....
Blue Moon by Frank Sinatra isn't exactly a recent number, and if this youth group is with other kids around 16, there's a really strong chance most of them won't have any idea who/what you're singing. Same with trying to take a girl by surprise into a dance number: chances are the only dances she knows are the slow-song-circle and the general motions for hip-hop from school dances.

I haven't got much for ideas you could replace them with; just that make sure you stay in your comfort zone for being outgoing; just try to make your plan a little more accessible to these girls you're trying to attract.

Hope this all made sense,

Tyler