La coda alla cassa è più lunga di quanto pensassi.

Yes, coda literally means tail, but it also very commonly means a queue or line of people waiting.

So in this sentence, la coda means the queue / the line. Italian often uses the same word for both ideas, and context makes the meaning clear.

Examples:

• Il gatto ha una lunga coda. = The cat has a long tail.
• C’è una lunga coda alla cassa. = There’s a long line at the checkout.

Yes, fila would also sound natural here.

• La coda alla cassa...
• La fila alla cassa...

Both can mean the line at the checkout. A small nuance:

• coda often emphasizes a queue of people or cars waiting
• fila is a broader word that can mean line, row, file

So both are correct, but coda is especially common when people are waiting their turn.

Alla cassa means at the checkout, at the cash register, or at the till, depending on the kind of English you use.

It is made of:

• a = at / to
• la cassa = the checkout / cash register

Together, a + la = alla.

So alla cassa is the normal way to say someone is at the checkout area in a shop or supermarket.

Because Italian usually uses a for being at a service point or location like this.

So you say:

• alla cassa = at the checkout
• al banco = at the counter
• alla reception = at reception

In cassa usually means something different, such as in the cash register, in the till, or even in the company’s funds/cash in business contexts. So for a customer waiting to pay, alla cassa is the natural choice.

Because lunga has to agree with coda, and coda is feminine singular.

So:

• la coda → feminine singular
• lunga → feminine singular form of lungo

That is why the sentence has:

• La coda ... è più lunga

If the noun were masculine, you would use lungo:

• Il film è più lungo di quanto pensassi.

Here, di quanto introduces the comparison: than I thought.

In a sentence like:

• più lunga di quanto pensassi

the idea is:

• more long than I thought
• more natural English: longer than I thought

So di quanto is a very common structure after comparatives such as:

• più ... di quanto = more ... than
• meno ... di quanto = less ... than

You can think of it as introducing the degree you had in mind before.

Sometimes yes, in everyday speech, you may hear similar paraphrases such as:

• più lunga di quello che pensavo

That is understandable and common in conversation. However, più ... di quanto ... is a very standard and elegant structure, and it is especially common in written or careful Italian.

So:

• più lunga di quanto pensassi = very standard
• più lunga di quello che pensavo = also natural, often a bit more conversational

Because after a comparative structure like più ... di quanto ..., Italian often uses the subjunctive when the second part refers to a personal impression, expectation, or mental judgment.

So:

• più lunga di quanto pensassi is a very good, standard sentence

That said, in everyday Italian, many speakers also say:

• più lunga di quanto pensavo

So for a learner, the useful takeaway is:

• pensassi is grammatically very good and somewhat more formal/careful
• pensavo is also common in speech

Pensassi is the imperfetto del congiuntivo — the imperfect subjunctive — of pensare.

Here is the form:

• che io pensassi
• che tu pensassi
• che lui/lei pensasse

In your sentence, it means something like than I thought / than I was expecting, inside a subordinate clause.

This form is often used after expressions involving:

• doubt
• opinion
• emotion
• comparison

Because Italian often leaves out subject pronouns when they are not needed.

So instead of saying:

• di quanto io pensassi

Italian usually just says:

• di quanto pensassi

That is normal and natural. The verb form often gives enough information, and context does the rest.

You can add io for emphasis, but it is not necessary.

Yes. That is possible.

The non in that kind of sentence is often called pleonastic non. It does not make the sentence negative. It is just an optional feature that appears in some comparative or formal structures.

So these can both work:

• più lunga di quanto pensassi
• più lunga di quanto non pensassi

In modern everyday Italian, the version without non is usually more common and simpler for learners.

Usually cassa means the checkout, till, or cash register — either the machine itself or the checkout point in the store.

It does not usually mean the person. The person is:

• il cassiere = male cashier
• la cassiera = female cashier

So:

• alla cassa = at the checkout
• la cassiera = the cashier

A little, yes, but not always naturally.

The original sentence is very clear because alla cassa stays close to coda:

• La coda alla cassa è più lunga di quanto pensassi.

If you move things around too much, the sentence may become less natural or slightly ambiguous. For example:

• La coda è più lunga alla cassa di quanto pensassi sounds less smooth and may make alla cassa feel attached to the wrong part of the sentence.

So for learners, the original order is a very good model to follow.

A rough pronunciation guide:

• La coda → lah KOH-dah
• alla cassa → AHL-lah KAHS-sah
• è più lunga → eh pyoo LOON-gah
• di quanto → dee KWAHN-toh
• pensassi → pen-SAHS-see

A few useful points:

• c before o in coda sounds like k
• ss in cassa and pensassi is a true double consonant, held a little longer than a single s
• più has the pyoo sound

So the whole sentence is approximately: lah KOH-dah AHL-lah KAHS-sah eh pyoo LOON-gah dee KWAHN-toh pen-SAHS-see