After gingivoplasty, what does the doctor keep in your mouth as bandaging/dressing, anything?

Perio Pack. Many peridontists were trained to use a periodontal packing after surgery that they place a the gum line. Not all use it. It is clinical judgement.
Zinc oxide paste. Not all gingivoplasty cases need dressing. Those done with lasers and no flap involvement do not requires sutures or packing to protect the wound from food. Extensive re-contouring of gingival lines and repositioning of tissue with flap involvement always require packing after suturing. The packing is typically pink soft to begin with hardening and removal approximately one week.
Perio- dressing. It's a dressing material that is used to keep the tissues clean and in place after the surgery.