If you bring small appliances, be careful. The shape adapter may not be enough. While basically all personal electronics in recent years will accept both voltages, some older, smaller appliances don't work with the hefty 220v in Europe. Check if the label near the appliance's power cord shows 100-240 v and 50-60 Hz. If it does not, you will need a "step-down transformer" (also called a converter).
The converter will reduce the 220 volts from the outlet to provide just 110 volts for the appliance. These converters cost a little more than simple adapters. Compare prices of converters here.
Tip: Don't bring any type of hair dryer to Iceland - they are awfully hard to match up with a suitable converter due to astronomical power consumption. Rather check if your accommodation in Iceland has one in the room, or just buy a cheap one locally.