Nach dem Frühstück räumen wir alles weg, aber den Kassenbon hebe ich für das Sonderangebot auf.

Because the preposition nach takes the dative case in this time expression.

• das Frühstück = nominative/accusative
• dem Frühstück = dative

So:

• nach dem Frühstück = after breakfast

This is a very common pattern:

• nach dem Essen = after the meal / after eating
• nach der Arbeit = after work
• nach dem Film = after the film

German main clauses follow the verb-second rule: the finite verb must be in the second position.

Here, the first position is taken by the time phrase:

• Nach dem Frühstück = position 1

So the finite verb must come next:

• räumen = position 2

Then the subject follows:

• wir

That is why you get:

• Nach dem Frühstück räumen wir alles weg

and not:

• Nach dem Frühstück wir räumen alles weg

This is very different from English, where the subject normally stays before the verb.

This is a separable verb: wegräumen.

In a main clause, separable verbs split:

• wir räumen alles weg

The conjugated verb stem goes in the normal verb position, and the prefix goes to the end.

Examples:

• Ich mache die Tür auf. = I open the door.
• Wir räumen alles weg. = We put everything away.

So:

• wegräumen = to clear away / put away

Alles means everything. Here it is the direct object, so it is in the accusative case.

In practice, alles looks the same in nominative and accusative, so there is no visible ending change here. But its role in the sentence is accusative because it is the thing being put away:

• wir räumen alles weg = we put everything away

Both are possible, but the version in the sentence gives extra emphasis or contrast to den Kassenbon.

German lets you move different elements into the first position of a main clause. When den Kassenbon comes first, it is highlighted:

• aber den Kassenbon hebe ich ... auf

This suggests something like:

• but the receipt, I keep

So the sentence contrasts:

• everything gets put away
• but the receipt is treated differently

Even after this fronting, the verb-second rule still applies, so the finite verb comes next:

• den Kassenbon = position 1
• hebe = position 2
• ich = after the verb

Because Kassenbon is the direct object of aufheben, so it must be in the accusative case.

Kassenbon is masculine:

• nominative: der Kassenbon
• accusative: den Kassenbon

So:

• Der Kassenbon ist wichtig. = The receipt is important.
• Ich hebe den Kassenbon auf. = I keep the receipt.

This is one of the most important masculine case changes to notice in German.

Here, aufheben means keep, save, or hold on to.

German aufheben can have different meanings depending on context, including:

• pick up
• save / keep
• sometimes even cancel/abolish in other contexts

In this sentence, because it is about a receipt and a special offer, the meaning is clearly:

• I keep/save the receipt

It is also a separable verb, which is why it appears as:

• hebe ... auf

instead of one single block in the main clause.

Because aufheben is another separable verb.

In a normal main clause:

• Ich hebe den Kassenbon auf.

The conjugated part (hebe) appears in the verb position, and the prefix (auf) moves to the end.

The same thing happened earlier with wegräumen:

• räumen ... weg

So the sentence contains two separable verbs:

• wegräumen → räumen ... weg
• aufheben → hebe ... auf

Für always takes the accusative case.

So:

• das Sonderangebot is accusative here

Sonderangebot is a neuter noun:

• nominative: das Sonderangebot
• accusative: das Sonderangebot

Because neuter nouns often look the same in nominative and accusative, there is no visible change.

Meaning-wise, für das Sonderangebot means something like:

• for the special offer
• for the promotion

In context, it suggests the receipt is being kept because it may be needed for that offer.

Der Kassenbon means receipt, especially a shop or checkout receipt.

It is a common everyday word in German. Depending on region and context, you may also hear:

• der Bon
• der Kassenzettel
• die Quittung (more general, often a receipt/proof of payment)

But Kassenbon very specifically sounds like the receipt you get at the cash register.

Because aber is connecting two main clauses, and in German these are usually separated by a comma.

The two clauses are:

1. Nach dem Frühstück räumen wir alles weg
2. aber den Kassenbon hebe ich für das Sonderangebot auf

So the comma helps mark the boundary between two complete clauses.

This is very normal German punctuation.

Yes. A more neutral version would be:

• Nach dem Frühstück räumen wir alles weg, aber ich hebe den Kassenbon für das Sonderangebot auf.

This version is grammatically fine and probably feels more straightforward to many learners.

The original version:

• aber den Kassenbon hebe ich ... auf

is more expressive because it brings den Kassenbon to the front for contrast.

So the difference is not grammar correctness, but emphasis and information structure.

Because some German verbs are built with separable prefixes, and those prefixes split off in certain sentence types.

For example:

• wegräumen
• aufheben
• anmachen
• einkaufen

In a main clause, the pattern is:

• conjugated verb near the front
• prefix at the end

Examples:

• Ich mache das Licht an.
• Wir kaufen heute ein.
• Er hebt den Bon auf.

But in an infinitive or with a modal verb, the verb usually stays together:

• Ich will den Bon aufheben.
• Wir müssen alles wegräumen.

This is one of the most distinctive features of German sentence structure.