Use a rubber band between the screw head and the screwdriver
Try a larger screwdriver bit that fits more tightly
Tap the screwdriver into the screw head with a hammer
Use a manual impact driver
Apply penetrating oil and wait a few minutes
Grip the screw head with locking pliers if it is exposed
Cut a new slot in the screw head with a rotary tool
Use a screw extractor bit
Drill a small pilot hole into the screw and use an extractor
Drill the screw head off if removal is the only option
Replace the screw with a new one after removal