A 30cm/12" extension to reach around larger pedals with a 2.1mm centre-negative barrel plug.
If you've got a particularly bulky pedal you might need a Black Adaptor to reach around and power it up. This is common with Wah pedals.
The Black Adaptor has a straight plug (instead of an angled plug like the Deluxe Daisy Chain) so you can link two or more together in a line without having an annoying kink in the cable.
Diago Black Adaptor Extension ~ 30cm