There are backpacks that have folding stools incorporated.
There are folding chairs with backpack straps.
The new ChairPack from BorgCo is better than both.
It's a backpack, or full size rucksack, which has a folding chair incorporated.
By leaning forward and pulling the release toggle,
the seat and legs hinge down under the wearer's lower body. By bending the knees and leaning back, the legs contact the ground, et viola ! The wearer is seated comfortably.
To stand, the user tips forward onto their feet, and presses the retract button; a small motor winds in the chair structure back into the backpack base.
The motor is powered by a lithium-ion battery which is kept charged by a photovoltaic panel, or can be externally charged via USB.