Hagas lo que hagas, no olvides mirar la fecha de caducidad antes de comprar nata.

This is a very common Spanish pattern meaning whatever you do.

• hagas = you do in the present subjunctive
• lo que = what / whatever
• So hagas lo que hagas literally works like do what you do, but idiomatically it means whatever you do.

The repetition is part of the fixed structure:

• digas lo que digas = whatever you say
• vayas donde vayas = wherever you go
• pase lo que pase = whatever happens

So hagas lo que hagas is not accidental repetition; it is the normal way to form this kind of expression.

The subjunctive is used because the sentence refers to an indefinite or non-specific situation: it does not say exactly what the person will do, only whatever it may be.

Spanish often uses the subjunctive in expressions like:

• sea como sea = however it may be
• venga quien venga = whoever comes
• cueste lo que cueste = whatever it costs / no matter the cost

So in hagas lo que hagas, the subjunctive helps express it doesn’t matter what action it is.

No olvides is the negative tú command of olvidar.

In Spanish:

• affirmative tú command: olvida
• negative tú command: no olvides

Negative commands for tú use the present subjunctive:

• No hables
• No comas
• No vivas
• No olvides

So no olvides means don’t forget when speaking informally to one person.

Because negative informal commands in Spanish are built with the present subjunctive.

For olvidar:

• indicative: tú olvidas
• subjunctive: que tú olvides
• negative command: no olvides

This is a general rule:

• No vayas = Don’t go
• No lo hagas = Don’t do it
• No compres eso = Don’t buy that

So no olvides is both a subjunctive form and the normal negative tú imperative.

Here lo que means something like what(ever).

In this structure, lo que introduces an unspecified thing or action:

• Haz lo que quieras = Do what you want
• Diga lo que diga = Whatever he/she says
• Hagas lo que hagas = Whatever you do

The lo here is not it. It is part of a very common structure where lo que means that which / what.

Both mirar and ver relate to seeing, but they are not the same.

• mirar = to look at
• ver = to see

In this sentence, the idea is to check / look at the expiry date deliberately, so mirar is the natural choice.

Compare:

• Mira la etiqueta = Look at the label
• Veo la etiqueta = I see the label

You could also hear comprobar la fecha de caducidad, which means check the expiry date and sounds a bit more explicit.

Fecha de caducidad means expiry date / use-by date. It is used for products that should not be consumed after that date for safety reasons.

It is not exactly the same as best before.

A useful distinction is:

• fecha de caducidad = use-by / expiry date
• fecha de consumo preferente = best-before date

On food packaging in Spain, both are common, but they mean different things. Caducidad is the stricter one.

After antes, Spanish normally uses de before an infinitive:

• antes de salir = before leaving
• antes de comer = before eating
• antes de comprar = before buying

So antes de + infinitive is the standard pattern.

You would use antes de que + subjunctive when there is a new subject:

• Antes de comprar nata, mira la fecha = Before buying cream, check the date
• Antes de que compres nata, mira la fecha = Before you buy cream, check the date

So in your sentence, antes de comprar is correct because it is a simple infinitive structure.

In Spain, nata usually means cream, especially dairy cream.

Examples:

• nata para cocinar = cooking cream
• nata montada = whipped cream
• fresas con nata = strawberries and cream

This is a good Spain-specific vocabulary point, because in some other Spanish-speaking countries people may more often use crema for some kinds of cream. In Spain, nata is the everyday word for the dairy product.

Because Spanish often leaves things unstated when they are already clear from context.

In English, you might expect something like before buying it, but in Spanish antes de comprar nata is completely natural and means before buying cream.

If you wanted to refer back to it, you could say:

• antes de comprarla

because nata is feminine, so la would be the object pronoun.

But repeating the noun directly, as in comprar nata, is also perfectly normal.

Yes. The sentence you have is informal, addressed to tú. A formal version for usted would be:

• Haga lo que haga, no olvide mirar la fecha de caducidad antes de comprar nata.

Changes:

• hagas → haga
• olvides → olvide

The structure stays the same; only the verb forms change to match usted.

Yes, definitely. It is very useful and very natural.

You can treat it as a set phrase meaning:

• Whatever you do
• No matter what you do

It is worth memorising because the pattern appears everywhere in Spanish:

• hagas lo que hagas = whatever you do
• digas lo que digas = whatever you say
• pienses lo que pienses = whatever you think

Learning it as a chunk will make it easier to recognise and later create similar sentences yourself.