NEVER leave the vehicle!
They are easier to spot in a search. You are SAFER staying put!
Water, shelter, food. Why leave your shelter? Your food and water will last you longer if you don’t exert yourself trying to hike out not to mention the possibility of injury.
STAY PUT! WAIT!
I’m not sure I’m buying the balloon idea. I don’t think it’s big enough to be seen from a search plane.
An orange trash bag or tarp would be better. Or a mylar emergency blanket. It would reflect the sun.
A friend is a former Navy rescue swimmer with tons of SAR experience. I’ll have to ask about the balloons.