I've been four times with mates for 4 or 5 nights each time. Still haven't been to the Grand Canyon despite planning on going each time. It would've eaten into gambling and drinking time.
Take plenty of cash for gambling. Haven't been for 4 years, but we found that it was really hard to find a (free) cash machine on the main strip.
Shopping etc can be done with cards, as you'd expect. Although exchange rate right now means that stuff is probably cheaper in UK, so stick to...