To put & hold prop in hand, U need to todo:
1) make a character hand pose like already holding prop in hand
In MB there is very usefull Align operation, which U can make up with dragging one object to another (from the context menu choose Align->Translation/Rotation).
2) add Parent/Child constraint, where use this setup – hand IK effector (LeftWristEffector) set as source object and prop object set as constrained.
3) Press Snap button in the constraint options pane
If U want to write motion from constraint to object position/rotation U need to execute plot operation. For this, select object and from main menu choose Plot Selected.