Find a way out
Once you've managed to escape into the building, head right to find a Coin 6/32 on the table, then go into the area ahead and take out some enemies. Now climb up the shelves and jump across to view a short scene, then you'll find yourself on the other side with a few enemies coming towards you.
Take them out and then go through to the garden center, here you'll find a Coin 7/32 on the counter and some Scrap laying around. Once you're done, head outside via the car to the back right, then help Manny up onto the rope on the left building. Wait a few seconds for him to extend the rope, then climb up and use the same rope to slide down into the building.
Free the door to allow Mel to come inside, then grab the Supplements scattered around before going into the next room. Now go through the gate and take two rights to find a workbench and some Scrap.
Tip: You'll want to use your first two upgrades on Stability and Capacity for the Semi-Auto Rifle.
Head to the roof
Once you're done upgrading, head up the stairs on the right to find some Supplements on the table, then attempt to open the gate. Due to the crank breaking you'll need to find a way up, so give Mel a boost up then go back up the stairs and wait for her to open the door.
Head through and use the ladder on the right to climb up onto the raised area on the right to find a Coin 8/32 and some Supplements, then drop down and use the ladder to get onto the boat. Before continuing, go inside the boat to find an Artefact.
Tip: Now that you've unlocked the Covert Ops Branch, you'll want to focus on unlocking the ability to craft shivs immediately, as this will allow you to one shot most enemies, and break free from a Clickers grasp.
Continue onwards to the FOB
Move the ladder to reach the otherside, then throw the rope over the path above and climb up. Take the ladder up to the roof, then climb down to meet up with Manny. Here you'll want to smash the Trailers window and climb in to find a Coin 9/32 and an Artefact 82/117, then crawl through hole to the left of the MS building.
Input the combination 17-38-07 into the safe to acquire some ammo and the Hunting Pistol, then go down to the tracks and carefully sneak past all the enemies using the trains as cover to reach the end of the path.
Once you've made it, climb up and head into the gas station, here you'll want to sit behind cover for a few minutes, then you'll get some backup.