The state of being high on marijuana. Not necessarily referring to a certain degree of high (ie: buzzing through baked), but often may be a specific style of relaxed, low-energy high. The etymological basis being the sound of weed crackling when smoked, typically because the weed is particularly dry (often occurring when smoked in a joint but can occur in most other smoking styles). The highs created from some dryer forms of cannibis.
This crackling sound frequently reminds one of the idea of a crispy texture, so it becomes a valid nickname on that basis, and it has a similar sound to the sound of Rice Krispies, the cereal, when they are mixed with milk, hence the spelling "Krispie(s)".
1: "Sup! I got Krispies man!"
2: "Want to go get Krispie?.. Now?"