In this video I went through an example of each bonus in Survival mode.
As few as 4 kills in rapid succession; decreases as time between kills increases.
4 kills without being hit by any enemy fire; resets if hit.
4 headshots during the same wave; does not reset.
5 knife kills in succession; resets if an enemy is killed with anything other than your knife.
Kill 5 flashed enemies during the same wave; does not reset if other kills are made between flash kills.
Kill 4 enemies with the same blast; can only be achieved with explosives, not with guns.