I went to the US last year.
Las Vegas and San Francisco. I took with me $700, but spent more.
Also pre booked some trips, but to be honest it would have been worth NOT pre booking as there are many tours on offer.
MY advice is, book the POPULAR one in advance and pay the extra, if its a trip in a life time then you dont want to miss out.
Helicopter rides: I really would pre book any way, due to the fact they cant hold many people in one go.
I pre booked a nice trip via With was a flight over the Hoover dam, a helicopter ride in to the grand canyon, a boat ride up the Colorado river and a bus to a couple of nice view points (one being where the Sky Walk is located.
it cost be about $300 from memory. But VERY worth the money!
www.alllasvegastours.com or www.allgrandcanyontours.com ( i think, google them) They offer some really great rates!
Who ever is going on this.....PLEASE PLEASE visit the Cheese Cake Factory! ..... *drools thinking about it* YUMMMMY indeed!!