The crates are unlocked by doing the special side.
Unlock locked doors dead rising 3.
While the zombies are your main enemy in dead rising 4 there will occasionally be moments where a door is standing between you and success.
Unlock doors dead rising 4.
The locked doors are all accessed by completing the main story and side missions which will give you access to all collectibles.
Unlock the doors is the second story mission during chapter 7 in dead rising 3.