Ek neem my reënjas en my handskoene saam as die weer skielik verander.

Because saamneem is a separable verb in Afrikaans.

The full idea is saamneem = take along / bring along.
In a main clause, the conjugated verb moves to the second position, and the separated particle goes to the end:

• Ek neem ... saam. = I take ... along.

Compare:

• Ek neem my reënjas saam.
• Ek wil my reënjas saamneem.

In the second example, after wil, the infinitive stays together as saamneem.

Because as die weer skielik verander is a subordinate clause.

In Afrikaans, subordinate clauses usually send the verb to the end. So:

• die weer verander skielik = main-clause style
• as die weer skielik verander = subordinate-clause style

This is very common after words like:

• as = if
• omdat = because
• dat = that
• wanneer = when

Here, as most naturally means if.

So the sentence means something like:

• I take my raincoat and my gloves along if the weather suddenly changes.

In some contexts, English might translate things a bit differently, but in this sentence if is the clearest match.

Do not assume Afrikaans as always matches English as exactly.

Afrikaans often repeats the possessive before each noun, especially when that sounds clearer or more natural.

So:

• my reënjas en my handskoene

is completely normal.

You may sometimes hear or see the possessive only once if the meaning is obvious, but repeating it is very common and natural.

Reënjas is a compound word:

• reën = rain
• jas = coat / jacket

So reënjas literally means rain coat, or raincoat.

The ë is there to show that the vowels are pronounced in separate syllables.
So reën is pronounced more like ree-en, not as one single vowel sound.

This kind of spelling mark helps show pronunciation in Afrikaans.

Handskoene is plural and means gloves.

The singular is:

• handskoen = glove

The plural is:

• handskoene = gloves

Literally, the word is built from:

• hand = hand
• skoen = shoe

So a handskoen is literally a hand-shoe.

Because die weer means the weather, and that is the normal phrase here.

Afrikaans often uses the definite article die in places where English might also use the:

• die weer = the weather

Also, weer by itself can mean again, so die weer makes the meaning very clear here.

Context tells you.

In this sentence, die weer clearly means the weather.
If weer meant again, the structure would be different.

For example:

• Ek neem dit weer saam. = I take it along again.
• Die weer verander. = The weather changes.

So when you see die weer, it is very often the weather.

Afrikaans often uses the present tense for things that are habitual, general, or understood from context, including future-like meaning.

So Ek neem my reënjas ... saam can mean:

• I take my raincoat ... along
• or, depending on context, I’ll take my raincoat ... along

English sometimes uses more explicit future wording, but Afrikaans often does not need to.

Yes, in many everyday situations you could hear vat instead of neem.

• neem = take
• vat = take / grab / take along

Neem is often felt to be a bit more neutral or standard.
Vat is very common in speech.

So a colloquial version might be:

• Ek vat my reënjas en my handskoene saam ...

But the sentence with neem is perfectly natural and standard.

Here, saam means something like along.

So neem ... saam means:

• take along
• bring along

On its own, saam can also mean together, depending on the sentence. But in saamneem, the meaning is specifically about taking something with you.

Skielik is an adverb meaning suddenly.

In this subordinate clause, placing skielik before the final verb is the normal word order:

• as die weer skielik verander

That is a very typical Afrikaans pattern: other information comes first, and the verb appears at the end of the subordinate clause.

It can match either one, depending on perspective.

Afrikaans saamneem often covers the general idea of taking something with you.
In English, whether you choose take along or bring along depends on viewpoint.

So this sentence could be understood as:

• I take my raincoat and my gloves along ...
• I bring my raincoat and my gloves along ...

If the meaning has already been given to the learner, that English choice is mostly a translation issue, not a grammar issue.