Travel Money - A mix of cash and card (depends how much poker you want to play, the more you want to play, the more cash I"d recommend). Avoid debit cards unless there"s an emergency. I"d recommend a Travelex cash passport (or similar currency card). No charges for ATM withdrawals, can reload online and not linked to your bank account. Credit card would be good if you can find one that doesn"t charge for FX, but it"s far more hassle than a currency card. You"ll probably need one to check in though.
GC/HD - Worth it, even if just to say "been there". Am told best way to see it is via helicopter. Myself and family did an excursion, minibus from the Strip, via Hoover dam to a ranch, bit of horse riding, then a helicopter flight from there. There are loads of trips available on the Strip, not sure which is best or whether it"s best to book prior - but don"t pay more than £200 (my excursion was most of the day and was around $200-250 I think a couple of years back. Hazy memory).
Car Hire - Don"t bother imo, there"s nowhere to go anyway. You"ll pay a surcharge if you"re under 25 I expect, but car hire out there is pretty reasonable if you do decide to take the plunge. Buses are frequent and easy to use, $7 per 24 hours. Only worth hiring a car for a day if you want to drive to a Wal-Mart to shop and save money on eating out, or to drive to the Hoover Dam/GC yourself.
Shows - There are discount ticket sellers on the Strip (Tix 4 Tonight). Get your tickets either the day before or on the day and you"ll have up to 50% off. Definitely don"t go via a box office. You can also get discounted buffet and restaurant vouchers. I"d recommend the Rio buffet, and Hugo"s Cellar downtown at 4 Queens ($3 will get you 25% off the total bill, and it"s incredible food + romantic old school atmosphere for your missus. They"ll give her a rose on entry so that"ll keep her happy I"m sure
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Downtown - Definitely worth going. It"s cheaper, dirtier and more genuine than the Strip. Freemont Experience (LED light show) every hour and free music on the stage there (not all year though). Get there via bus.
Attractions - Don"t do the CSI Experience, or the Treasure Island buffet. Woeful. Depends on your tastes, but you won"t struggle to find stuff to do, free or otherwise.