This page of the guide to Far Cry 6 contains a walkthrough of Operation Packing Heat , one of the main missions in the Madrugada region. You will learn e.g. where the ammo truck is, how to steal it and how to successfully deliver the vehicle to Philly.
Steal the ammo truck for Philly
You can start this operation after completing the main quest Second Son. You must return to the rebel camp at the Montero Farm to meet Philly Barzaga. Agree to help him the the ammo.
Unlike the Second Son quest, this time you'll get directions to a specific location - Ocaso Marina - where the ammo truck you must steal is located.
Once you get there, focus on eliminating all the enemies in the area. Doing a recon would be a good idea, as well as killing the enemies from a hill with a suppressed weapon. You can also release a wild animal from the cage.
If you are going to engage in more direct combat, avoid using explosives that could damage or destroy the truck. Also, don't stand too close to the truck during fights, especially since one of the enemies has a rocket launcher.
Deliver the truck to Philly
Enter the truck when the fights are over. You're going to have to get it to Philly in good condition and that's why it was important to secure the marina in advance.
Leave the hostile location and avoid driving into large obstacles (breaking barriers or small fences should not affect your damage bar) and hitting/alarming enemies to avoid an unwanted chase. Parking your vehicle in the marked spot will complete this short mission.