Često zaboravljam ponijeti punjač sa sobom.

This is a very common Croatian pattern: a finite verb + an infinitive.

• zaboravljam = I forget / I keep forgetting
• ponijeti = to bring / take along

So zaboravljam ponijeti means I forget to bring / take along.

Croatian often uses the infinitive after verbs like moći (can), morati (must), željeti (want), zaboraviti/zaboravljati (forget), etc.

Because the Croatian present tense is also used for habits and repeated actions, not just for what is happening right now.

Here, često means often, so the whole sentence means a habitual action:

• Često zaboravljam... = I often forget...

So this is not necessarily I am forgetting right now. It is this happens to me often.

This is mainly about aspect.

• zaboravljati / zaboravljam = imperfective
• zaboraviti / zaboravim = perfective

In this sentence, zaboravljam sounds natural because it emphasizes a repeated habit or tendency.

You may also hear Često zaboravim... in everyday speech. That is not wrong; it presents each forgetting as a complete event. But for a learner, zaboravljam is a very clear way to express I often forget as a general habit.

So:

• zaboravljam = I keep forgetting / I have a habit of forgetting
• zaboravim = I forget, viewed as a whole event

After zaboravljam, Croatian uses the infinitive of the action that is forgotten.

So:

• zaboravljam ponijeti = I forget to bring/take along

Here ponijeti is perfective, because bringing the charger is seen as one complete action each time.

That combination is normal:

• an imperfective verb for the repeated habit: zaboravljam
• a perfective infinitive for the single action: ponijeti

ponijeti means to take along / bring with you.

In English, depending on context, this may be translated as either bring or take along. Croatian does not always match English bring vs take in exactly the same way.

Here it means something like:

• to remember to have the charger with you when you leave

So ponijeti punjač is the natural choice for bring/take the charger along.

These verbs are related, but they are not the same.

• ponijeti = take/bring along with you, especially on one occasion
• nositi = carry, wear, or regularly have on you
• uzeti = take, pick up

In this sentence, ponijeti is the best choice because the idea is taking the charger with you when you go somewhere.

Compare:

• Zaboravio sam ponijeti punjač. = I forgot to bring/take along the charger.
• Nosim punjač sa sobom. = I carry the charger with me.
• Uzeo sam punjač. = I took the charger.

Because punjač is the direct object, so it is in the accusative case — but for a masculine inanimate noun, the accusative singular is the same as the nominative singular.

So:

• nominative: punjač
• accusative: punjač

That is why the form does not change.

Compare with a masculine animate noun, where it would change:

• pas → vidim psa

But:

• punjač → ponijeti punjač

sa sobom literally means with oneself, but in normal English it usually means with me / with yourself / with him-/herself, depending on the subject.

In this sentence, the subject is I, so:

• sa sobom = with me

Croatian uses the reflexive pronoun sobom when the person referred to is the same as the subject.

So:

• Nosim punjač sa sobom. = I carry the charger with me.
• Ona nosi dokumente sa sobom. = She carries the documents with her.

If you mean a different person, you use a normal pronoun:

• sa mnom = with me
• s tobom = with you
• s njim = with him

The basic preposition is s, meaning with.

But Croatian often uses sa instead of s before words that begin with certain sounds, especially s, š, z, ž, or awkward consonant clusters, because it is easier to pronounce.

So:

• sa sobom sounds natural and standard

This is the same preposition, just in a pronunciation-friendly form.

Yes, often you can.

• Često zaboravljam ponijeti punjač.

This already sounds natural and may be enough if the context is clear.

Adding sa sobom makes the meaning more explicit:

• not just take the charger
• but take it along with me

So the full version is slightly more specific, but both are possible.

No. Croatian word order is fairly flexible.

The original sentence is a very natural neutral order:

• Često zaboravljam ponijeti punjač sa sobom.

But other orders are also possible, for example:

• Zaboravljam često ponijeti punjač sa sobom.
• Često zaboravljam sa sobom ponijeti punjač.

These alternatives may sound more marked or put focus on a different part of the sentence. For learners, the original order is a very good default.

sobom is the instrumental singular form of the reflexive pronoun sebe.

That is because the preposition s/sa normally takes the instrumental case.

So:

• sa sobom = with oneself

This is a useful phrase to learn as a whole, because it is very common in Croatian.