Havasupai - Campground to Beaver Falls O/B
Recommend this hike on day 2 unless you need to go into town on day 2 for something necessary. Bring gloves, don't bother with hiking poles, water shoes are nice for the crossings but you'll be at risk of blisters if you keep them on the whole way.
Bring a picnic along for hanging at the Beaver Falls grounds, it's pretty and swimming in the waters are refreshing.
1-2 liters of water bottles + filter are more than enough to get you to the falls, plenty of places to refill safely with ice cold water.
If you plan to continue onto the rapids, start really early or you'll be climbing up a cliff face in the dark, that hike is long and slow.