You can't do a proper deadlift without weight. And I think that is the single most useful strength exercise out there. Most amount of weight, works whole body, thus your whole CNS and your mind.
But google calisthenics, they do strength training with bodyweight. E.g. pistol squat is insanely hard and useful for Cycling I guess. Calve workouts can be done with bodyweight, too, core of course, all useful for cycling.