The DS1054z does _not_ have selectable 50 ohm input impedance, all channel inputs are fixed at 1 Megohm.
It looks like that kit1 includes 2 50-ohm feedthrus, one the Rigol part and one the CT brand part.
Some of the cables/adapters will be more useful with your FG and DMM than with the scope, but yes, all those items are good to have on hand.