Mind your paperwork.
Counterfeiting of Peruvian nuevo sol notes and the American dollar is such a big worry in Peru that merchants will eye your paper money the way pawn brokers squint at unconvincing diamonds. The tiniest rip will kill a transaction, and you'll end up stuck with a bill that you can't use.
The other paper issue is bathroom-specific. The Peruvian custom is to put used toilet paper in wastebaskets and not to flush it. If you flush it, you could cause a plumbing crisis.
Give the Sacred Valley more time.
There is about 70 miles of valley between Cuzco and Machu Picchu, and it's not enough to make quick, crowded stops at the ruins and town of Ollantaytambo and the Sunday market at Pisac. Head up to the underappreciated ruins at Pisac. Better yet, head for the salt mines of Maras.
The best thing about Maras might be getting there: You'll probably take a taxi, guide's car or minibus, and soon you'll be rambling up unpaved roads into the middle of a green Peruvian dream of barley and potato fields, ox-drawn plows, wandering sheep and Quechua farmers. Especially for those who aren't doing a multiday trek, this is a great taste of the countryside.
When you do finally reach the salt mines, you'll see hundreds of evaporation ponds carved in the red dirt and filled with saline water from a nearby spring. As the water evaporates, salt is harvested every month or so. The revenue has sustained local families for centuries.
Many guides like to combine Maras with the nearby Moray archaeological site, a series of terraced, concentric circles that were apparently used as a pre-Columbian agricultural laboratory. The valley is full of options, including the rustic town of Chinchero; the luxurious Sol & Luna Spa & Lodge (www.hotelsolyluna.com) in Urubamba; the bungee jumps and paragliding of Action Valley (www.actionvalley.com); and the challenges of the Natura Vive via ferrata (www.naturavive.com), a dramatic climbing route with cables to ease your ascent.
All these places are within about 40 miles of Cuzco. If you buy a Boleto Turistico del Cusco (about $50), it will cover the cost of admission to Moray, Pisac, Ollantaytambo, Sacsayhuaman and several other ruins and museum sites. If you have more time than money, you can cut costs by waiting to book day trips until you arrive in Cuzco. Once here, gather fresh references from other travelers and question a few outfitters. They'll be easy to find, especially in the storefronts surrounding the Plaza de Armas.