Because gaffers tape is made from woven cotton cloth, it can be hand torn. No cutting tools required.
Nothing sticks to tape like tape. Be careful to not let the sticky side of a piece of tape touch more of the same sticky side. It will create a permanent bond and the tape will be unusable.
Gaffers tape can be torn both cross wise and length wise. It is easy to start with a roll of two inch tape and create a narrower piece.