So which items can be equipped at same time?
Can you equip Symbiote and Eclipso to same character? Or Supreme Intelligence and Proteus? Weapon Drop and Brainiac?

A character can only have one equipped item at a time. The Supreme Intelligence is not equipped. I'd recommend reading the "Equip" section of the E&C thread on the WIN, there's a link in my sig.

Thank you I need a new rulebook

It's coming soon!

yes, a new rulebook which includes these terms will be very helpful.

please note that the Book of the Skull, which uses the word "equip", is an entirely different mechanism, so you could have Parallax "equipped" to a Superman and equip that Superman with a hammer from the Book.