If your Toyota Camry trunk won't open, one possible reason is that it is set to valet mode. Valet mode means that you cannot open the trunk using the release lever inside the car.
To set valet mode, you put the key into the trunk lock and turn it counterclockwise. You will know that your trunk is in valet mode if the lock is horizontal rather than vertical, and if you cannot open the trunk using the lever near the driver's seat.
Of course, a problem is that sometimes the Camry can get stuck in valet mode, such that you can't use your key to get out of it. (You can see how I spent part of my Sunday morning ...)
The solution turns out to be WD-40. Spray some WD-40 on your key and on the lock. Put the key in, and jiggle it around, and happiness ensues.
From an interaction design perspective, it sort of makes sense to have a valet mode. After all, the point of having a valet key is to limit the functions that an untrusted person can use. On the other hand, in the roughly 20 years I've driven a car, I pretty much never remember to bring the valet key with me, and have only valet parked at most three times. I suspect valet mode has caused more problems than actually solved.