The purpose of this study is to evaluate a drug called pafolacianine that attaches to cancer cells and lights up when seen through a special camera system. The study focuses on patients who have gastrointestinal cancer (gastric, esophageal, or appendiceal) or whose study doctor suspects they may have gastrointestinal cancer, and who will be undergoing surgery as a part of treatment. Participants will receive pafolacianine; during surgery, the study team will turn on the camera to evaluate whether the tumor is visible with the help of the study medication. Researchers will measure the location of the tumor before and after use of the special camera and document their findings. Pafolacianine could help the study doctor see the cancer better during the surgery, which may help her/him take out more of the cancer. The use of pafolacianine in this study is considered investigational.