Isto não era para ficar na bagageira; era para levares o croissant contigo.

Isto is a neuter demonstrative pronoun meaning this.

It is often used when:

• you are pointing to something without naming it first
• you are referring to a whole situation
• the noun has not been introduced yet

So Isto não era para ficar... is like saying This wasn’t supposed to stay...

Why not the others?

• este usually links more directly to a masculine noun, for example este croissant
• isso usually points to something closer to the listener, or something the other person has just said

So isto sounds very natural here.

Here, ser para + infinitive means to be supposed to, to be meant to, or to be intended to.

So:

• não era para ficar na bagageira = it wasn’t supposed to stay / be left in the boot
• era para levares o croissant contigo = you were supposed to take the croissant with you

This is a very common Portuguese structure. It does not mean something like it was for staying in a literal word-for-word sense.

Era is the imperfect of ser.

In this pattern, era para often refers to an expectation, plan, or instruction that existed before the present moment. It often implies that the plan was not followed.

So the idea is:

• that was the plan
• but it did not happen correctly

Compare:

• É para levares = you are supposed to take it now / this is what you should do
• Era para levares = you were supposed to take it

Foi para would usually mean something different, more like went in order to in other contexts, so it would not fit well here.

Here ficar means to stay, to remain, or to be left somewhere.

So ficar na bagageira means:

• stay in the boot
• remain in the trunk
• be left in the car boot

This is very natural Portuguese. It suggests the croissant ended up there and should not have.

In Portugal, a bagageira usually means the boot of a car.

In American English, that would be the trunk.

So:

• na bagageira = in the boot / in the trunk

This is a good word to know because it is standard in European Portuguese. In Brazilian Portuguese, porta-malas is more common.

Because Portuguese normally contracts em + a into na.

So:

• em + a = na
• em + o = no

Since bagageira is feminine singular, you get:

• na bagageira

This kind of contraction is extremely common in Portuguese.

Levares is the personal infinitive.

Portuguese has a special infinitive form that can show who the subject is. After para, that is very common.

Here:

• levar = basic infinitive
• levares = infinitive marked for tu

So era para levares means specifically:

• you were supposed to take

If you used levar, the subject would be less explicit. Levares makes it clear that the person being spoken to is the one who should have taken the croissant.

Portuguese often leaves out subject pronouns because the verb ending already shows the subject.

In the personal infinitive:

• levar = I / he / she / you formal
• levares = you singular informal, tu
• levarmos = we
• levarem = they / you plural

So the ending -es tells you the hidden subject is tu.

That is why era para levares naturally means you were supposed to take.

After com, Portuguese uses special pronoun forms.

So:

• comigo = with me
• contigo = with you, informal singular
• consigo = with him/her/you formal

That means:

• contigo is correct
• com tu is not correct

So levares o croissant contigo means take the croissant with you.

Portuguese uses definite articles more often than English.

Here o croissant means a specific croissant that both speaker and listener already know about. In English, you might just say take the croissant with you, and Portuguese does the same with o.

Also, croissant is commonly treated as a masculine noun in Portuguese, so:

• o croissant

That is why o croissant sounds normal and natural here.