#2. Make it a military map. Civilian maps are usually not very good for navigating terrain. Contour lines help you pick out defensible high ground.
#3. As soon as you can, break into a military post. Take several M4A1 carbines, some with the grenade launcher accessory, and a bunch of magazines. Also take an M249 SAW in case you need to spray down a crowd. Then get several cases of 5.56mm and some boxes of 40mm grenades. Might not hurt to get an M1014 combat shotgun with some ammo if you can find one.
#5. Hummer. Hard top, but not armored (zombies don’t use guns). You need the military version, which is called a Humvee, NOT the civilian Hummer, which is based on a standard GM SUV platform. Grab one while you’re on post, and grab a trailer for it too (they don’t use civilian trailer hitches). Make sure it has a turret ring for your M249. Don’t forget the extra 5-gallon gas cans.
#11. Food. While on post, grab as many MREs you can fit into your trailer while you’re getting those water tablets.
#12. Night vision. While on post, get night vision. Both for your face and as scopes for your guns.
#13. Some hose, bolt cutters and a hand-crank pump. You’ll need it to refuel from gas station tanks.