Yup. AJ is right. Play Zombies with friends in a party and there won't be a problem.
I knife only at the 1st round. Then i use my pistol on the 2nd round with the shoot 'n knife combo. Then i buy the M14 off te wall. When i got enough points, i use it to open doors to help my team, and save my points first for Juggernog. Which will help me later on for bigger waves.
You can save your points too for Speed cola and Stamin-up if you want.
When insta-kill is on, use your knife only. Especially when Double points is also active with it. You'll get like 260 for each kill. Don't waste bullets. Not in every round a max ammo will drop.
I never spam the box, only if i get a Sniper or RPG. People spam the box only for the Raygun. Until a teddybear comes up... Fire sale is ok for spamming the box. Because it's only 10 points in that limit and on every location. Save your points for Pack-a-punch.
And please stay in game. There's no need to leave when things going wrong. Especially in parties. Only when it's important like: Going for dinner or something else important.
Oh, and if you have a mic, use it!