Cuando viajo, llevo toallitas en el bolso por si no hay jabón.

Because this sentence describes a habitual action: something the speaker generally does whenever they travel.

• Cuando viajo = When I travel
• llevo toallitas = I carry wipes
• por si no hay jabón = in case there isn’t any soap

In Spanish, the present tense is often used for habits and general routines, just like in English.

If the speaker were talking about one future trip, they would more likely say:

• Cuando viaje, llevaré toallitas... = When I travel / On my next trip, I’ll take wipes...

So the original sentence sounds like a general personal habit.

This is a very common question.

• Cuando + present indicative is used for habitual/repeated actions.
• Cuando + present subjunctive is used for future actions that have not happened yet.

So:

• Cuando viajo, llevo toallitas... = Whenever I travel, I take wipes.
• Cuando viaje, llevaré toallitas... = When I travel / When I go on my next trip, I’ll take wipes.

In your sentence, the meaning is whenever I travel, so viajo is correct.

Toallitas is the diminutive form of toallas.

• toalla = towel
• toallita = little towel / wipe
• toallitas = wipes

In everyday Spanish, especially in Spain, toallitas often means wet wipes or cleansing wipes, even if húmedas is not added.

You may also hear:

• toallitas húmedas = wet wipes

So in this sentence, toallitas most naturally means wipes.

Because en means in or inside, and here the wipes are located inside the bag.

• llevo toallitas en el bolso = I carry wipes in my bag

The preposition a would not work here, because a usually indicates direction or a personal object, not location inside something.

In Spain, bolso usually means a handbag, purse, or a personal bag someone carries.

Depending on context, English bag could be translated in different ways:

• bolso = handbag / purse / personal bag
• mochila = backpack
• maleta = suitcase
• bolsa = shopping bag / plastic bag / sack

So en el bolso suggests the person keeps the wipes in the bag they carry with them, not in luggage.

Because por si means in case, while si by itself means if.

• por si no hay jabón = in case there isn’t any soap
• si no hay jabón = if there isn’t any soap

These are close in English, but not the same in Spanish.

Por si expresses a precaution:

• I take wipes in case there’s no soap.

It explains why the speaker takes wipes.

Because after por si, Spanish normally uses the indicative, not the subjunctive.

So:

• por si no hay jabón = correct

This is because the speaker is thinking about a real possibility and taking precautions for it.

English learners often expect the subjunctive after expressions like in case, but Spanish works differently here.

Compare:

• Llevo toallitas por si no hay jabón. = I take wipes in case there isn’t soap.

So hay is the normal and expected form.

Because jabón here is being used as an uncountable substance noun in a general sense.

• no hay jabón = there isn’t any soap

This is very natural in Spanish. You do not need un or el here.

Compare:

• No hay jabón. = There’s no soap.
• No hay agua. = There’s no water.
• No hay papel. = There’s no paper.

If you added an article, the meaning would change or sound less natural in this context.

Yes, you can, but the nuance is slightly different.

• llevo toallitas = I carry wipes / I take wipes
• llevo unas toallitas = I carry some wipes / a few wipes

Without the article, the sentence sounds more like a general habit or a general category of item.
With unas, it sounds a bit more concrete, as if you mean some specific wipes.

Both are possible, but the original version is very natural.

Because Spanish often omits subject pronouns when the verb ending already makes the subject clear.

• viajo already means I travel
• llevo already means I carry

So:

• Cuando viajo, llevo... is completely normal.
• Cuando yo viajo, yo llevo... is possible, but usually unnecessary unless you want emphasis or contrast.

Spanish uses pronouns much less often than English.

The comma separates the introductory time clause from the main clause:

• Cuando viajo, = introductory clause
• llevo toallitas en el bolso... = main clause

This helps readability and is very common in writing.

In short sentences, you may sometimes see variation, but using the comma here is standard and clear.

Yes, but it works a little differently.

• por si no hay jabón = in case there isn’t any soap
• por si acaso = just in case

Por si acaso is more general and does not state the specific problem.
The original sentence is more precise because it tells you exactly what the concern is: that there may be no soap.

You could say:

• Cuando viajo, llevo toallitas en el bolso por si acaso.

That means:

• When I travel, I carry wipes in my bag just in case.

Both are natural, but the original is more specific.

Usually no, not in this context.

• llevar = to carry / take
• traer = to bring

Spanish often distinguishes these based on direction or point of reference.

Here, the idea is that the speaker takes or carries the wipes with them while travelling, so llevo is the natural choice.

Traigo would usually mean I bring, often toward the place where the speaker is or toward the listener, which does not fit as well here.