You can do this using QMAKE_BUNDLE_DATA. All you need to do is define your files and where you want to put them in the bundle. qmake will take care of the rest.
Here's an example where we add a framework to the bundle
# Rest of the .pro file
PRIVATE_FRAMEWORKS.files = /path/to/MyFramework.framework
PRIVATE_FRAMEWORKS.path = Contents/Frameworks
QMAKE_BUNDLE_DATA += PRIVATE_FRAMEWORKS