W mojej torbie zawsze jest mała apteczka, więc mam tam też chusteczki i maść.

Because w meaning in (when it shows location, not movement) requires the locative case.

So:

• moja torba = my bag (dictionary/basic form)
• w mojej torbie = in my bag

Both the adjective and the noun change:

• moja → mojej
• torba → torbie

This is a very common pattern in Polish:

• w domu = in the house
• w szkole = in school
• w mojej torbie = in my bag

They express two slightly different ideas.

• W mojej torbie zawsze jest mała apteczka = There is always a small first-aid kit in my bag
• więc mam tam też chusteczki i maść = so I also have tissues and ointment there

So:

• jest is used for there is / there are or something is located somewhere
• mam means I have

In English, both can sometimes sound similar, but Polish often separates these ideas more clearly:

• W torbie jest apteczka = There is a first-aid kit in the bag
• Mam apteczkę w torbie = I have a first-aid kit in my bag

Both are possible, but they focus on slightly different things.

Because jest refers only to mała apteczka, which is singular.

The sentence has two parts:

1. W mojej torbie zawsze jest mała apteczka
2. więc mam tam też chusteczki i maść

In the first part, the subject is:

• mała apteczka = singular

So Polish uses:

• jest = is

If the first part were about several objects, then you would use są:

• W mojej torbie zawsze są chusteczki i leki = There are always tissues and medicines in my bag

Apteczka usually means first-aid kit.

Although it looks like a diminutive form, in modern Polish it is the normal everyday word for a small box, pouch, or set of medical supplies used for emergencies.

Examples:

• apteczka samochodowa = car first-aid kit
• apteczka domowa = home first-aid kit

So in this sentence, mała apteczka means a small first-aid kit.

Because in Polish, adjectives usually come before the noun they describe.

So:

• mała apteczka = small first-aid kit
• moja torba = my bag

This is the normal order in everyday Polish.

Putting the adjective after the noun is possible in some special styles, but it is not the neutral everyday pattern.

Więc means so, therefore, or thus.

It connects the two ideas:

• There is always a first-aid kit in my bag,
• so I also have tissues and ointment there.

It shows a result or logical consequence.

Other common connectors with similar meanings include:

• więc = so
• dlatego = therefore / that’s why
• zatem = therefore / thus, a bit more formal

Tam means there, and here it refers back to w mojej torbie.

So:

• mam tam też chusteczki i maść = I also have tissues and ointment there

It is not absolutely necessary, but it makes the location explicit and natural.

Without tam, the sentence would still work:

• W mojej torbie zawsze jest mała apteczka, więc mam też chusteczki i maść.

That would mean roughly:

• There is always a small first-aid kit in my bag, so I also have tissues and ointment.

With tam, the speaker clearly reinforces in there / in that bag.

Też means also or too.

In this sentence:

• mam tam też chusteczki i maść
• I also have tissues and ointment there

Its position is quite natural in Polish. Word order in Polish is more flexible than in English, and też often appears close to the element it relates to.

Here it adds the idea that, besides the first-aid kit, there are additional useful things in the bag.

You may also hear similar sentences like:

• Też mam apteczkę. = I also have a first-aid kit.
• Mam też wodę. = I also have water.

They are in the accusative case because they are the direct objects of mam.

The verb mieć = to have usually takes the accusative.

So:

• mam chusteczki
• mam maść

For these particular nouns, the forms happen to look like this:

• chusteczki — this form is the same in nominative plural and accusative plural for non-masculine-personal nouns
• maść — this feminine singular noun has the same form in nominative and accusative

So even though the case is accusative, the words do not visibly change here.

Chusteczki usually means tissues or wet wipes, depending on context.

The singular is:

• chusteczka

The plural is:

• chusteczki

In a sentence about a bag or first-aid supplies, many learners will naturally understand chusteczki as tissues or possibly wipes.

The exact English translation can depend on context.

Maść means ointment or salve.

In Polish, it is typically treated as an uncountable substance noun in sentences like this:

• mam maść = I have ointment

If you want to refer to a specific tube or container, Polish can express that more explicitly, for example:

• mam tubkę maści = I have a tube of ointment

But by itself, maść simply means the substance.

Yes, in some contexts w swojej torbie could also be possible, but w mojej torbie is simpler and more direct.

• mojej = my
• swojej = one’s own

Polish often uses swój when the possessor is the same as the subject of the clause. However, in this sentence the first clause begins with a location phrase and the subject is really mała apteczka, so mojej is very natural and straightforward.

For learners, w mojej torbie is the easiest and safest version to understand and use.

Yes. Zawsze means always, and its position is natural.

• W mojej torbie zawsze jest mała apteczka

This means:

• In my bag, there is always a small first-aid kit

Polish adverbs like zawsze, często, czasem often have flexible placement, but this sentence sounds normal and idiomatic.

For example, these are all possible, though with slightly different emphasis:

• W mojej torbie zawsze jest mała apteczka
• Zawsze w mojej torbie jest mała apteczka
• Mała apteczka zawsze jest w mojej torbie

The original version is very natural.

Yes. For example:

• W mojej torbie zawsze mam małą apteczkę, więc mam tam też chusteczki i maść.

This is grammatical, but it changes the feel a little.

Compare:

• W mojej torbie zawsze jest mała apteczka
  Focus: the first-aid kit is a regular item found there.

• W mojej torbie zawsze mam małą apteczkę
  Focus: I make sure to carry it.

So the original version sounds a bit more like describing what is in the bag, while the rewritten version sounds a bit more personal and intentional.