My breakfast is milk,bread and sausages.
"My breakfast" is a singular noun, but "milk,bread, and sausages" are plural noun phrase.
Is this sentence right?
"is" is a form of "be"
third person singular present of be.
"be" can mean "composed of"
Consist of; constitute:
Therefore we can say that:
My breakfast is milk, bread, and sausages.
My breakfast consists of milk, bread, and sausages.
In cases like this, simply think for yourself: which word(s) is/are the subject of the sentence?
The verb is conjugated according to the subject. In this case,
my breakfast is the subject, so the sentence is indeed correct. In fact, all of the following are correct.
My breakfast is milk, bread and sausages.
My breakfasts are milk, bread and sausages.
Even the following is correct, with
Milk, bread and sausages being the subject. However, this sentence sounds strange, so you will not hear it very often:
Milk, bread and sausages are my breakfast.