Las Vegas during the summer is excruciatingly hot, so number one in your packing list should be lots of sun block. Bring at least two bathing suits, comfortable clothes and shoes and sandals. Most nighttime places are casual in Vegas but some restaurants do have a dress code. A fancy outfit and pair of shoe is a must for those restaurants with dress codes or for a night at the club. For your day outings, always have a bottle of water with you. A nice hat is also not a bad idea.
If you happen to visit Las Vegas during winter, don't be fooled. Vegas may not be known to get blizzards, but it gets a lot colder there than you think. Bring a jacket and warm clothes and footwear.
Don't forget to bring a camera to capture those enchanting shows and your unforgettable moments. Most importantly, bring lots of cash for those slot machines. Remember, what happens in Vegas stays in Vegas!