The theme for last week was reaction, quickness and speed (which could be paraphrased as "explosive response").
On the pell, put a 2" square of different colored tape on each side of the "head" and on each "thigh".
1) The striker stands on-guard (use a shield) and says ready to the referee.
2) The referee waits a random 1-5 seconds and shouts "Go!".
3) The striker explodes their shot to hit the 2" target.
4) Repeat steps 1-3.
5) Repeat steps 1-3.
... (after 10 strikes at target)
12) Change target to the next tape mark and repeat 1-3.
13) Repeat 1-3.
...
42) Switch people and start over.
This yields 40 shots per person, 10 each at the four tape marks. The on-guard position does not need to remain the same, in particular, for the different targets.
Things to keep in mind:
This drill should occur early in the practice session when everyone is fresh. There should be some warmup work first (maybe 5 minutes of light striking combos per person). If you think the striking technique looks incorrect during the drill, work with that person to correct the technique in future practice sessions, before more training sessions.