how does everyone determine how many calories/portions they are consuming? by weight, palm/fist size?

does anyone ever get the munchies in the evening especially for junk food? why is this?

how does everyone determine how many calories/portions they are consuming? by weight, palm/fist size?
Depends on the food, I have food scale and measuring cups. Generally nutritiondata.com or the packaging of the food will tell you the serving size. You can use the above mentioned measuring devices to dole out a serving (or half a serving, or 3 servings, whatever fits your caloric needs).

does anyone ever get the munchies in the evening especially for junk food? why is this?
Sure, but instead eat something clean.

Late night cravings are usually caused by lack of proper nutrients during the day. People who dieted too strictly and deprive themselves too much usually experience this.
To avoid it, keep healthy food always available so that when the cravings attack, you can grab healthy options.
Keep your house clean of junk foods, because when the craving attack and you have junk foods around you, there is a greater chance that you'll grab those instead.
Late night craving is more of a symptom rather than a problem, fix the problem first (lack of needed nutrients). Be careful, because it's consider as a bad habit that'll make you gain weight...