First of all, i have to say that this is my opinion.
A prerequisite is that you have a private server. They are cheap so support this game and get one
Outlands Old | "Secret Spawn" (Map ID 14)
Loot everything in this Area, maybe go to the near Airfield and loot there a bit. Log out restart your Server and join again. There will be everywhere good and fresh new loot.There are a huge amount of Stanag Weapons and also there can be rare Weapons. Like Famas DDPAT, QBZ, LS 90 and Snipers as well.
I think it the best way to farm weapons, ammo and attachments.
Money and XP:
Caliwood | "The Street" (Map ID 4)
Go to the Street i showed in the Location Pic. There is a Shop where you have to jump on. Zombies dont come up there and you can kill them easily with a melee weapon. Except a SZ (Super Zombie). WATCH OUT ! There are a lot SZ´s. Maybe 5-6. Lure them and go in the shop they dont come up there but you need a Gun to kill them because they punch you if you are to close.
Tipp: In this street are about 15 Item Boxes !
District9 | "Heli-Crash Crossing" (Map ID 20)
One Run there:
Loot everything around the Heli Crash, even the Bulidings ! Best to farm Armors. Weapons and Meds are also very good there.
I dont know a location where its good to farm them. The best thing i know is killing zombies at Caliwood. So while you farm Money and XP with my guide, zombies will drop a good amount of Bandages DX. (Also Weapons)
Maybe later i will find a good place. And then i will insert it to this guide
If i find other good places later i will tell you
Good looting !