In regards to the collision detection; the CustomMovement doesn't collide with Solid objects. I would recommend utilizing either an 8'directional movement, or car behaviour, for it to collide. Edit it within events to get it feeling very 'astronaut'.
Now, to get the character to hold an object, you're going to have to make a boolean instance variable called IsHoldingObject, and by default set it to FALSE. Also set a PIN behaviour to the boxes, and add in an image-point in the astronaut's animations, where he would normally 'hold' the objects.
Now, when the astronaut collides with a box, it checks if the astronaut [not]IsHoldingObject, and then sets the position of the collided box to the image-point (that I mentioned earlier) of the astronaut. Then, pin the box to the astronaut, and set IsHoldingObject to TRUE.
You can have a particular button which will drop the crates, such as the space-bar. When that key is pressed, make it check if IsHoldingObject = true, and if so, unpin the NEAREST (to the astronaut's image-point) crate.
Also, the crates should all have physics, with no gravity, on them. That's how they'll bounce realistically.