Camping equipment can be rented in a number of stores near Plaza de Armas, as well as from most of the tour agencies located on Plateros and Procuradores streets.
Prices vary, but you can expect to pay $3-5 for a tent, $3 for a sleeping bag, $2-3 for a stove (all per day) and another $1.5 for fuel. All rentals require a deposit in cash, plus a credit card or passport. Quality varies so choose carefully.
The best place to rent is Soqllaq'asa Camping Service, located at Calle Plateros 359, tel. 252560. Service is friendly, English-speaking, and they will even buy equipment you no longer need.
Gear can also be purchased at Camping Deportes, Av. del Sol 346, shop # 118.
Food for the hike can be purchased at a good supermarket on the corner of Almagro and Av. del Sol.