Event items are items created specially for a specific the Event and are usually used as a currency. They can be everything from footballs, funny animals, jewels, tokens, cakes or everyday items.

Since a specific event will most probably never be duplicated, event items can not be used again after the event ends.

It's generally a good idea to use those items during the exact event they are designed for, unless you just want to keep them as a souvenir.