Builders of sheet metal airplanes know to buy a gazillion clecos so that they can hold their plane together for riveting. Well, we composite builders have equivalents -- dry wall screws! I use dry wall screws typically to hold pieces of foam together while fit-checking, gluing, and glassing. Dry wall screws have the advantages of holding things very securely without causing damage to cores like nails, bondo, or dabs of 5-minute glue.
In this picture I'm using the dry wall screws to hold the pilot's armrest together during fit-checking.