Invitation to the Game by Monica Hughes
And we scrounged. Next to survival, scrounge was probably the most important word in our new vocabulary. We found a store that was throwing out water-damaged mattresses. Getting them home was a problem, since we had to make two trips, leaving Brad and Katie, armed with sticks to guard over the remained. I truly expected them to be challenged by some gang boss, but they said that the only person who came by was a scrawny little rat of a girl living alone. We let her have one of the mattresses.