I'm working from memory here, so I am sure I'm getting some things wrong or missing some stuff

1. Announce plans for a vigil for the dead to take place at the town plaza with the Sheriff in attendance. Major Calar will report this back to the cartel after his 5:00 visit and they will target the assembly. 

2. Repair one or two discarded vehicles (pickup truck and tiller). Prepare one of them as a car bomb using home made explosives. 

3. Set up mannikins from an abandoned clothes shop in the park to create the illusion of a crowd.

4. Ignacio sets up a sniper's roost in the church belltower. Bishop sticks close to the Sheriff in the plaza. Cooper waits in a vehicle at an intersection. Tess waits in her trans am at the end of the Highway. Cesar hides near the fence overlooking the schoolhouse and playground. Somebody (?) prepares the car bomb at another intersection.

5. When the anticipated cartel vehicle approaches the plaza, the car bomb is sent into it, ideally pinning it near the abandoned schoolhouse and killing or incapacitating most of the passengers. Cooper drives to block their escape and Tess drives in help further hem them in.

6. Ignacio, Bishop, Cesar and the Sheriff open fire on the boxed-in cartel gunmen, killing as many as possible.