Search for a good analogy in the real world for the mathematical concept of set I looked for a good explanation of a set for a course. Therefore I want to find a good analogy of this concept in real life. First I thought of explaining the set as something like a container such as a box. But a box has an identity regardless of its content, i.e. the box stays the same if its content changes. In contrast the identity of a set depends highly on its elements. If you add an object to a set you get a new one.
Second thoughts were something like a school class or a band. But also a school class remains the same if a new pupil joins the class during the year and band members can change.
Do you know a good analogy of a set in real life – some kind of collection which changes (or we think of it as to be a new collection) if its elements changes?
To explain the concept of sets I want to say: "A set is something like ..." And ... shall be something everyone knows from his everyday life.
 A: As Mauro points in the comments, the analogy of the box is good, but you take it one step too far. The importance is not the box itself but rather its content. Sets are the mathematical realization of "the content of the bag", rather than the bag itself.
This means that in order to find a nice analogy you should probably look for something in the real world which is well-defined, but not bound by a physical object somehow. For example, families. Your immediate family (parents, siblings) is a well-defined concept. If someone had the same parents and the same siblings as you, then they have the same family. That is to say, if two families have the same members then it's the same family.
A: You should think a set like a collection of things with a common property and the restriction that not all properties are allowed.For example, the set of numbers that are even. To be even is an allowed property. On the other hand, you should already know that $\{x∣x∉x\}$  is not a set, cause this property is not allowed. For more information, any text in basic set theory would be helpfull.
If you want an example in real world, we could say,the set of humans being mathematicians ,i.e. a set of things, people, satisfying certain property. 
A: Its not perfect, but: imagine you're cooking a stir fry.
A set is like an ingredient list; if you add or remove some items, it is not the same. On the other hand, if you merely change the order in which the ingredients are written, that's okay.
