Along with water, willpower and a strong pair of legs, a backpack is what almost every undocumented immigrant carries through the Sonora Desert.

Miles from the nearest store or restaurant, unable to cook on a camping stove for fear of attracting attention and under the searing heat of the sun in the day, migrants take a mix of lightweight nibbles, medicines, sweets and electrolyte solution to help them make the trip.

At the main supermarket in Altar, an impressive, well-stocked store for such a humble place, we spoke to poor Mexicans preparing to walk the desert who were buying food for their trip. Here is what is most of them put in their backpack, which can be bought for $5 at any of a dozen stores that line the shabby town`s streets.

A couple of tins of tuna

A packet of electrolyte powders, a vital combination of sugar and salt to avoid or recover from dehydration

A kilo of raw brown sugar

Packets of beef jerky

Garlic

Gatorade

Chocolate bars

A packet of tortillas

Two gallons of water

Undocumented migrants rub the raw garlic on their trousers to keep snakes, scorpions and coyotes away.  Some take energy drinks such as Red Bull, although taking the drink is counterproductive, the Red Cross in Altar says, as it means people dehydrate more rapidly. The days of carrying wads of cash in backpacks to help an illegal immigrant is his or her new life are over, as bandits cruise the desert and seek to rob the migrants.

Like would-be migrants from across Mexico, we spent $15 each on supplies of food and water for the three-day trek. We also shopped around and bought long-sleeved shirts, cotton neckscarves and baseball caps for shelter from the sun, and a $5 rug to sleep on the desert floor. Total cost, $16.

REUTERS photos by Tomas Bravo