The unused output pins of general-purpose logic IC must be open.
However, for pins that may become inputs (such as bus pins) like bi-directional bus buffers such as 245, please connect both ends of the input and output to the power supply or GND via pull-up/pull-down resistors. To avoid unnecessary current flow, it is recommended to pull up or pull down both ends of the bi-directional bus buffer to the same potential.
The following documents also contain related information.