Nemoj da zaboraviš torbu i kišobran.

To make a negative command to one person, Serbian very often uses nemoj + da + present tense.

• nemoj = don’t
• da zaboraviš = literally something like that you forget

Together, the whole phrase simply means don’t forget.

So:

• Nemoj da zaboraviš = Don’t forget
• Nemojte da zaboravite = Don’t forget (plural or formal)

You may also hear the shorter Ne zaboravi, but nemoj da + present is a very common everyday pattern.

Zaboraviš is the 2nd person singular present tense form of zaboraviti (to forget).

So the verb forms are:

• ja zaboravim = I forget
• ti zaboraviš = you forget
• on/ona zaboravi = he/she forgets

After nemoj da, Serbian uses a present-tense form, even though the meaning is not really present time. It expresses the action that the speaker is telling someone not to do.

Because torba is the direct object of the verb zaboraviti. In Serbian, direct objects usually go in the accusative case.

• nominative: torba
• accusative singular: torbu

So:

• torba = bag
• zaboraviti torbu = to forget the bag / a bag

Because kišobran is a masculine inanimate noun. In Serbian, masculine inanimate nouns usually have the same form in the nominative and accusative singular.

• nominative: kišobran
• accusative: kišobran

So it is in the accusative here too, but its form does not visibly change.

Because both nouns are objects of the same verb, zaboraviti.

The conjunction i means and, and it joins two direct objects:

• torbu
• kišobran

Since zaboraviti takes the accusative for the thing being forgotten, both nouns appear in the accusative.

Serbian does not have articles.

So:

• torbu can mean a bag or the bag
• kišobran can mean an umbrella or the umbrella

The exact meaning depends on context.

This is a question of aspect, which is very important in Serbian.

• zaboraviti = perfective
  one completed act of forgetting

• zaboravljati = imperfective
  repeated, habitual, or ongoing forgetting

In this sentence, the speaker means one specific future mistake: forgetting the bag and umbrella. That is why zaboraviti is natural.

Compare:

• Nemoj da zaboraviš torbu. = Don’t forget the bag.
• Nemoj da zaboravljaš torbu. = Don’t keep forgetting the bag.

It is talking to one person, informally.

You can tell from:

• nemoj = singular informal
• zaboraviš = singular informal

If you were speaking to more than one person, or speaking formally to one person, you would say:

• Nemojte da zaboravite torbu i kišobran.

Yes. Serbian word order is fairly flexible.

The original sentence is a very neutral and natural order:

• Nemoj da zaboraviš torbu i kišobran.

But you could also say:

• Nemoj da zaboraviš kišobran i torbu.
• Torbu i kišobran nemoj da zaboraviš.

The meaning stays basically the same, but the emphasis can shift.

Not necessarily. In everyday Serbian, Nemoj da... is often just a normal reminder or warning.

Depending on tone of voice, it can sound like:

• a friendly reminder
• practical advice
• a stronger instruction

So in many real situations, Nemoj da zaboraviš torbu i kišobran is simply the natural way to say Don’t forget your bag and umbrella.