My best strategy is this:
Spend 1st and 2nd shooting each zombie 6 and 8 times respectfully then knife them (when out of ammo just knife). After the 2nd round open the door on the right and buy the PM63 (unless the box is there). Use all your ammo (if you got the box leave when it does) then go downstairs and buy the MP40 (unless box is there or you have 2 better guns from the box) and continue to the stage (not enough points? stay till you do.) Spend one round holding off in the theater and turn the power on when you have 2500+ points. Buy jug and connect the teleporter. If the box isn't in a room you have spend your points opening the door(s) to them. Get in the teleporter and kill the last zombie. At the start of the round use the teleporter and throw grenades, when you come back throw a grenade at the lobby double doors, and start a circuit around the map, that's basically the whole thing. I made it to 29, and here's the list of importance for buying things:
Jug
1 decent Pack-a-Punched gun
Speed Cola
2 decent Pack-a-Punched guns
Claymores
Double Tap (only if you have a heavy MG or shotgun)
Ray gun and Thundergun, both Pack-a-Punched
At some point the Ray Gun will not have enough ammo to last you between dogs/max ammo. When this happens you have two options basically:
1: Take a random gun and PaP (you must get 5950 with each gun)
2: Take a gun that makes a lot of points off the wall, PaP and keep coming back for more ammo (you must get 4500 between refills, but the guns aren't as good)
Hope this helps! :D
