I'm not great with EoC and therefore I may not be aware of everything that is available in actions bar. You can either link any ability you want to or it can be an inventory area (this assists in OSRS GP clearing logs, and also eating). If you'd like linking an ability, go to the tab range/melee/magic on the interface, and move one of your combat capabilities to the bar for action.
Drag an inventory space onto it, if you wish to connect it in the Action Bar. I'm not sure you can connect summoning scrolls with it however, I...
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