You do not have to replace them with identical articles. Grab bags MUST be purchased at they time they are advertised. If you don't order immediately, you may lose that special kit. When you buy something, use it before you read the directions. Begin getting your loved ones accustomed to the fact that you intend to be buried with your models.
Plastic models are an inexpensive hobby.
This can be proved by applying male logic to your modeling purchases. This just makes sense. Every modeler MUST own every type of glue that is on the market. However, he may restrict use to his favorites. Whenever a new paint line is made available, you must immediately purchase every one of the colors in which it comes.