Cost: 500 on solo and 1500 on multiplayer. Quick revive is the is the cheapest perk and most essential on single player. it functions differently in solo and Co-Op gameplay. In solo mode when you get downed by a zombie and you have the quick revive perk you are brought back to life in roughly ten seconds you are equiped with pack a punched pistols (grenade launcher bullets).in Co-Op it lets your team mate revive you 3x times faster.
Jugger-nog is based on the infamous multiplayer juggernaut perk, jugger-nog is vital to surviving in the solo modes. it allows you to rush past a group of zombies and still survive if you get hit a few times. The jugger-nog perk allows you to get out of most tricky situations, it is vital for surviving later rounds. Jugger-nog is also very useful in hellhound modes, if you partner gets down you can revive him with out needing to worry aout getting down.
Double Tap allows you to fire your gun at a significantly faster speed. This can be a great upgrade for slow firing weapons, like the M16, but its not so good for high rate of fire weapons like the AK74U.
Speed Cola is the first upgrade you should really try to get after youturn on the power and get your first Pack-A-Punch upgrade. It halves your reload time, making it less likely for you to get caught between clips as you face down the undead hordes.
Pack-A-Punch is the ultimate upgrade and its usually hardest to access. Feed it a normal weapon, and spits out a super upgraded version of that weapon. The upgraded weapons have larger clips and better damage all things vital for making it in to the double digit rounds.