The Pennsylvania Supreme Court has held that police may search the personal effects of a visitor (not on the person) to the premises pursuant to a valid search warrant to search the premises if the personal effects were a part of the general content of the room and a plausible repository for the object of the search.
Commonwealth v. Reese, 520 Pa. 29, 549 A.2d 909 (1988).
Frank H. Bole,
Search and Seizure - Searching Personal Effects of a Visitor to the Premises Where a Valid Search Warrant Is Being Executed,
Duq. L. Rev.
Available at: https://dsc.duq.edu/dlr/vol28/iss2/9