W małej portmonetce trzymam monety, kartę i paragon z wczorajszych zakupów.

Because after w meaning in, Polish normally uses the locative case.

So:

• mała portmonetka = a small coin purse nominative, dictionary form
• w małej portmonetce = in a small coin purse locative

Both the adjective and the noun have to change:

• mała → małej
• portmonetka → portmonetce

This is very common in Polish:

• w dużym domu = in a big house
• w dobrej kawiarni = in a good café

Portmonetce is in the locative singular.

The noun portmonetka is a feminine noun ending in -ka. In the locative singular, many nouns of this type change like this:

• -ka → -ce

So:

• portmonetka → w portmonetce
• książka → w książce
• szafka → w szafce

This is a normal sound-and-ending change in Polish declension.

Trzymać literally can mean to hold, but in many contexts it also means to keep or to store something somewhere.

So in this sentence, trzymam is more like:

• I keep
• I have stored
• I keep inside

That is why W małej portmonetce trzymam... sounds natural: it means you keep these things in the coin purse.

If you said mam, that would mean I have, but it would not express the idea of keeping them in that place as clearly.

They are the direct objects of trzymam, so they are in the accusative case.

Here is what happens:

• monety = accusative plural of moneta
• kartę = accusative singular of karta
• paragon = accusative singular of paragon

For masculine inanimate nouns like paragon, the accusative singular is often the same as the nominative singular:

• paragon → paragon

But feminine nouns usually change:

• karta → kartę
• moneta → monetę singular

Since monety is plural, that is the plural direct-object form here.

Because karta is a feminine singular noun, and in the accusative singular, feminine nouns ending in -a usually change to -ę.

So:

• karta nominative = card
• kartę accusative = card as a direct object

Other examples:

• mam książkę = I have a book
• widzę kobietę = I see a woman
• biorę torbę = I take a bag

This is one of the most important Polish patterns to learn.

Because the sentence refers to coins in the plural, not one coin.

Compare:

• trzymam monetę = I keep a coin
• trzymam monety = I keep coins

Here monety is the plural form. For this noun, the nominative plural and accusative plural are the same because it refers to non-masculine-personal things.

It means from yesterday’s shopping or from yesterday’s purchases.

It describes paragon:

• paragon z wczorajszych zakupów = a receipt from yesterday’s shopping

So z here means from, not with.

The phrase tells you what kind of receipt it is: the receipt that comes from those purchases.

Because the preposition z meaning from/out of requires the genitive case.

The basic form is:

• zakupy = shopping, purchases

After z, it becomes:

• z zakupów

And because wczorajszych describes zakupów, it also has to be in the genitive plural:

• wczorajszych zakupów

So the whole phrase is grammatically matched.

In Polish, zakupy is very commonly used in the plural to mean:

• shopping
• purchases
• the things bought

This is completely normal. Polish often uses plural forms where English uses a singular mass noun.

Examples:

• Idę na zakupy. = I’m going shopping.
• wrócić z zakupów = to come back from shopping
• paragon z zakupów = a shopping receipt / a receipt from purchases

So wczorajszych zakupów is the natural expression.

Not exactly.

• portmonetka usually means a small coin purse or change purse
• portfel usually means a wallet

A portmonetka suggests something small, often for coins, maybe also a card and a receipt in this sentence.

So the sentence gives a very specific image: a small purse or pouch where someone keeps coins, a card, and a receipt.

Yes. Polish word order is fairly flexible, because case endings show grammatical roles.

The original:

• W małej portmonetce trzymam monety, kartę i paragon z wczorajszych zakupów.

This puts emphasis first on where the items are kept.

You could also say:

• Trzymam monety, kartę i paragon z wczorajszych zakupów w małej portmonetce.

This is also correct, but it sounds a bit more neutral in structure.

Polish speakers move parts around for emphasis, rhythm, or style.

Because Polish has no articles.

English distinguishes:

• a small coin purse
• the small coin purse

Polish does not use separate words for that. Context tells you whether something is definite or indefinite.

So:

• w małej portmonetce can mean in a small coin purse or in the small coin purse, depending on context.

Yes.

• wczoraj = yesterday
• wczorajszy / wczorajsza / wczorajsze = yesterday’s

In the sentence, it has to agree with zakupów genitive plural, so it becomes:

• wczorajszych

This is a good example of how Polish often turns time words into adjectives:

• dzisiejszy = today’s
• jutrzejszy = tomorrow’s
• wczorajszy = yesterday’s

So wczorajszych zakupów literally means of yesterday’s purchases.