Other than the prearranged drills mentioned, the most common fighting drill we work with is, of course, "command kumite", or , initialy, one step right hand attacks.
The first level just uses a right hand attack, and allows the defender to practice his timing and counters that might not be used in the multitudinous prearranged drills we have, which are all good, but in which memorization must often overlay reflex.
It seems a simple matter to then increase the single attack to two.
Then perhaps go to punch, counter, block of counter etc.
Another appraoch is to dictate, initially, the attack and counter, as the depth of going off line for a punch is different that that one would use when using a "roundhouse kick" as a counter, for example.
Just some thoughts in an attempt to get this forum going.
Of course, everyone is going to think his or her prearranged one or two step drills as very good, and they probably are.
On prearranged drills, as noted, we stick primaralily, thus far, with Yakusoku (1). Kumite 3, amd Kumite One, but I hope to reintroduce Dan as Sensei Mike has done.
I think GEM once said two things of great worth:
"once your are past your third attack, you should think seriously before going furhter."
"Not going "offline" is a 'dead man's habit".
"All Enlightenment Gratefully Accepted"