Use a small flathead screwdriver in the hex socket
Use a Torx bit that fits snugly in the hex socket
Use needle-nose pliers to grip the head if it protrudes
Use locking pliers to turn the fastener if accessible
Use a slightly oversized hex wrench from another set
Use a precision screwdriver set with hex bits
Use a coin or thin metal edge if the fastener is loose enough
Use a rubber band for extra grip with a makeshift tool
Use a drill bit shank that matches the socket size
Use a small adjustable wrench on the outside of the bolt head if applicable