I think most rocks and crates are already movable, you just need to push at them a little harder, or find someone stronger to do it for you (which is usually the better way :oP)

You might try making a Bumped() proc, which works like this:

First, declare the new proc, which you want attached to all objects, turf, obj, and mob, so make it an atom proc.

atom/Bumped() return // does nothing by default

Next, you want the Bumped() proc to be triggered when that objected is Bumped by something. Now, all movable atoms come with a Bump() proc already, which is triggered when they bump into something. So, we'll just modify the Bump() proc a little to trigger the Bumped() proc for whatever got bumped.

atom/movable/Bump(atom/O)
..() // continue with default behavior
O.Bumped(src) // call Bumped() for whatever got bumped into, and the src inside the () tells it what it was bumped by.

After that, modify the Bumped() of the rock or crate so that it will move.

obj/crate/Bumped(atom/movable/M)
..()
Move(src,M.dir) // move the create in the direction that the object which bumped it is facing.

And that should do it.