Ya llevo planificadas las vacaciones de agosto, pero todavía no he reservado el hotel.

Here llevar + past participle/adjective expresses the idea of having something already done by this point.

So ya llevo planificadas las vacaciones de agosto means something like:

• I already have my August holidays planned
• I’ve already planned out my August holidays

It does not literally mean I carry planned. The verb llevar often has extended meanings in Spanish, and one of them is this idea of having something done so far.

A similar pattern would be:

• Llevo leídos tres capítulos = I’ve read three chapters so far
• Llevo preparadas dos maletas = I’ve got two suitcases packed already

Because planificadas agrees with las vacaciones, which is:

• feminine
• plural

So the participle/adjectival form has to match:

• vacaciones → feminine plural
• therefore → planificadas

Compare:

• Llevo planificado el viaje = I’ve got the trip planned
  (viaje = masculine singular)
• Llevo planificadas las vacaciones = I’ve got the holidays planned
  (vacaciones = feminine plural)

In this structure, the participle behaves a lot like an adjective, so agreement is important.

In Spanish, vacaciones is normally used in the plural, even when English would use singular vacation.

So:

• Me voy de vacaciones = I’m going on vacation
• Las vacaciones de agosto = the August holidays / the vacation in August

This is just the standard Spanish way of expressing the idea.

Las vacaciones de agosto means the August holidays or the holidays in August.

Using de + month is very common to identify something by the month it belongs to:

• las rebajas de enero = the January sales
• el calor de agosto = the heat of August
• las vacaciones de agosto = the August holidays

Other options would change the nuance a little:

• vacaciones en agosto = holidays in August
• vacaciones para agosto = holidays planned for August

In your sentence, de agosto sounds natural because it labels which holidays we are talking about.

Because the sentence is contrasting something already done with something not done yet.

• ya = already
• todavía no = not yet / still not

So the speaker is saying:

• ya llevo planificadas las vacaciones de agosto = I already have the August holidays planned
• pero todavía no he reservado el hotel = but I still haven’t booked the hotel

This creates a very natural contrast:

one part is done, another part is still pending

In Spain, the present perfect (he reservado) is very commonly used for past actions that are still connected to the present moment.

Here, the idea is:

• up to now, I haven’t booked it

So todavía no he reservado el hotel is very natural in Peninsular Spanish.

In much of Latin America, many speakers would more often say:

• todavía no reservé el hotel

Both can be understandable, but for Spanish from Spain, no he reservado is especially typical.

It can correspond to both ideas in English depending on context:

• I haven’t booked the hotel yet
• I still haven’t booked the hotel

Todavía no literally suggests that the action has not happened up to now, but it may still happen later.

Examples:

• Todavía no he comido = I haven’t eaten yet
• Todavía no lo sé = I still don’t know / I don’t know yet

So here it implies that booking the hotel is still pending.

In Spanish, it is very common to use the definite article when referring to a specific thing understood from context.

So he reservado el hotel means:

• I’ve booked the hotel

This suggests a particular hotel relevant to the trip.

If you said he reservado un hotel, that would mean:

• I’ve booked a hotel

That sounds less specific.

Spanish usually does not drop the article in this context the way English sometimes does.

Yes, and it is a very useful comparison.

• Ya tengo planificadas las vacaciones = I already have the holidays planned
• Ya llevo planificadas las vacaciones = I already have the holidays planned / I’ve already got the holidays planned so far

Both are natural, but llevo planificadas adds a slight sense of progress up to this point. It feels a bit more like as of now, this part is already done.

So:

• tengo planificadas = more neutral, state
• llevo planificadas = state plus a sense of progress so far

Planificar is correct and understandable, but depending on the speaker and context, other verbs may sound more everyday or more idiomatic, such as:

• organizar
• preparar
• tener pensado

For example:

• Ya tengo organizadas las vacaciones de agosto
• Ya tengo preparadas las vacaciones de agosto
• Ya tengo pensadas las vacaciones de agosto

That said, planificadas is perfectly fine, especially if the speaker wants to stress that the trip has been carefully planned out.

Yes. It is a useful pattern in Spanish.

Llevar + past participle/adjective often means to have something done so far or to be this far along with something.

Examples:

• Llevo hechas dos tareas = I’ve done two assignments so far
• Llevamos recorridos cien kilómetros = We’ve covered one hundred kilometres so far
• Lleva escritas diez páginas = She has written ten pages so far

A key thing to notice is that the participle usually agrees with the noun:

• hechas with tareas
• recorridos with kilómetros
• escritas with páginas

So your sentence is a very good example of this pattern.

Yes, they could be reversed:

• Todavía no he reservado el hotel, pero ya llevo planificadas las vacaciones de agosto.

That is also correct.

The original order puts the focus first on what has already been done, and then contrasts it with what is still missing. That feels very natural because the speaker is presenting their planning progress and then mentioning the unfinished part.

So the order helps shape emphasis, but both versions are grammatically fine.

Pero means but and marks a contrast between the two ideas:

• the holiday plans are already sorted
• the hotel is still not booked

Without pero, the sentence would sound less clearly contrasted. With pero, the speaker is highlighting that these two facts coexist:

I’ve done a lot already, but one important thing remains undone.