Tip 1: Get self-revive if you're playing solo, ASAP. Otherwise, try and save up for Juggernog and Speed Cola.

Tip 2: Turn on the power behind the curtain to start your path to the Pack-A-Punch. Now go to the teleport (at the front of the stage), activate this, then head to the very first room you started in and activate the glowing pad.

Tip 3: The random weapon box is the most cost-effective way of buying new guns in the main. Most of the items you'll find inside are far better than the ones on the wall.

Tip 4: The only negative is that you will run out of ammo eventually. If you're close to saving up the 5000 for a Pack-A-Punch, use it to give you a completely new clip.

Tip 5: The final dog always drops a Max Ammo pick-up. This can be an absolute blessing on the later waves.