Of course it is unrealistic to expect that any college student will obtain a degree without missing at least one class, but you should try and minimize the number of classes you miss so that you get the best college education possible.
If you miss class and there is a very good reason then simply tell the truth. Many professors have heard all of the excuses before, and can tell when you are lying. As long as you do not make a habit of missing classes most of your professors will understand the occasional situation. If there was a family emergency you can usually get verification of this fact. This verification can include a note from a physician or medical facility, or it can be a program from a funeral service if a relative or close friend has died. Providing verification to your professors will show that the excuse is genuine, and you did not miss because you were out partying all night.
If you missed class because of poor or unacceptable reasons then you feel the need to lie about the reason , but if you do use caution. Lying is not a good choice for a number of reasons. If you are discovered then the professor may mistrust you from that point on. If you use the excuse you had a family emergency and it is not true then