Prima di partire, compro un sacchetto di mangime per le anatre del parco.

Because after prima di in Italian, you normally use an infinitive.

• prima di partire = before leaving
• prima di mangiare = before eating
• prima di dormire = before sleeping

So di is required here. Prima partire would sound incorrect.

Partire means to leave or to depart.

In this sentence, prima di partire means before leaving or before I leave.
Italian often uses the infinitive where English might use a full clause like before I leave.

Italian often uses the simple present to talk about:

• habitual actions
• scheduled actions
• near-future actions

So compro literally means I buy, but depending on context it can also mean:

• I’m buying
• I buy
• I will buy

In this sentence, it can naturally mean something like Before leaving, I buy a bag of feed... or I’m buying... before leaving, depending on the situation.

Un sacchetto di mangime means a bag of feed.

Italian often uses a container expression:

• un sacchetto di... = a bag of...
• una bottiglia di... = a bottle of...
• un chilo di... = a kilo of...

So:

• mangime = feed / animal feed
• un sacchetto di mangime = a bag of feed

Both are grammatically possible in different contexts, but this sentence specifically says a bag of feed.

Mangime means feed, especially animal feed.

It is used for animals, not people.

Compare:

• cibo = food (general, often for people, but can be broad)
• mangime = feed for animals

So because the sentence is about ducks, mangime is the natural word.

Per means for, and le anatre means the ducks.

So:

• per le anatre = for the ducks

Anatre is the plural of anatra. Since anatra is feminine, the plural definite article is le:

• l’anatra = the duck
• le anatre = the ducks

Italian uses articles more often than English.

So where English might say:

• for ducks
• for the ducks

Italian will often prefer:

• per le anatre

In this sentence, le anatre sounds natural because it refers to a specific group: the ducks at the park.

Del parco means of the park.

It is made from:

• di = of
• il = the

These combine into:

• di + il = del

So:

• le anatre del parco = the ducks of the park
• more natural English: the ducks in the park / the park ducks

Italian often uses di + article where English may prefer a different structure.

Both are possible in Italian, but they mean slightly different things.

• le anatre del parco = the ducks of the park / the park’s ducks
• le anatre nel parco = the ducks in the park

In this sentence, del parco identifies which ducks we mean: the ones associated with the park.

So del parco is acting like a description of the ducks, not just stating where they happen to be.

It describes le anatre, not mangime.

So the structure is:

• un sacchetto di mangime = a bag of feed
• per le anatre del parco = for the ducks of the park

That means:

I buy a bag of feed for the park ducks,
not a bag of park feed.

Because prima di partire is an introductory phrase.

Italian often puts a comma after a phrase at the beginning of a sentence, especially when it sets the time or context:

• Prima di partire, compro...
• Dopo cena, usciamo.
• Se vuoi, ti aiuto.

The comma helps separate the introductory part from the main clause.

The sentence breaks down like this:

• Prima di partire = before leaving
• compro = I buy
• un sacchetto di mangime = a bag of feed
• per le anatre del parco = for the ducks in/of the park

So the structure is:

time phrase + verb + object + purpose/recipient phrase

This is a very common and natural Italian word order.

Yes, in informal writing you may see it without the comma, and it would still be understood.

However, with an introductory phrase like Prima di partire, the comma is very common and helps readability. So the version with the comma is a good model to follow.

Sacchetto is masculine singular, which is why it uses un:

• un sacchetto = a bag

A few clues:

• words ending in -o are often masculine
• the article un also shows it is masculine singular

Its plural is:

• sacchetti = bags

Yes. Partire can mean:

• to leave
• to depart
• to set off

The best English translation depends on context. If someone is beginning a trip, before setting off can sound very natural.