Σήμερα θα φτιάξω σαλάτα με τόνο και σάντουιτς με γαλοπούλα για το ταξίδι.

Θα φτιάξω means I will make / I will prepare.

In Modern Greek, the future is usually formed with θα + a verb form, rather than with a special future ending like in some languages. So:

• φτιάχνω = I make / I am making
• θα φτιάξω = I will make

So Σήμερα θα φτιάξω... means Today I’ll make...

This is about aspect, which is very important in Greek.

• θα φτιάξω = I will make it as a single, complete action
• θα φτιάχνω = I will be making / I will make habitually

In this sentence, the speaker is talking about one planned action today, so θα φτιάξω is the natural choice.

Yes, it could go elsewhere. Greek word order is fairly flexible.

Putting Σήμερα first gives the time frame right away: Today. That is very natural. You could also say something like Θα φτιάξω σήμερα..., but the original order is a very common neutral way to say it.

Greek does have words that can mean a / one — ένας, μία, ένα — but they are not always used where English would use a.

With food and other direct objects, Greek often leaves the noun bare when the exact indefiniteness is not important. So θα φτιάξω σαλάτα is a natural way to say I’ll make salad / a salad.

You could also say μια σαλάτα if you want to make one salad more explicit.

Με means with.

Here it introduces the ingredient or filling:

• σαλάτα με τόνο = salad with tuna
• σάντουιτς με γαλοπούλα = sandwich(es) with turkey

After με, Greek uses the accusative case.

Because τόνος is the dictionary form, but after με the noun goes into the accusative.

So:

• ο τόνος = the tuna
• με τόνο = with tuna

This is a normal change for many masculine nouns ending in -ος:

• ο φίλος → τον φίλο
• ο δρόμος → τον δρόμο

Because many feminine nouns ending in -α have the same form in the nominative and accusative singular.

So:

• η γαλοπούλα = the turkey
• με γαλοπούλα = with turkey

The case still changes grammatically, but the word itself does not look different here.

Σάντουιτς is an indeclinable loanword, so the form is often the same in both singular and plural.

That means context has to tell you the number.

For example:

• ένα σάντουιτς = one sandwich
• δύο σάντουιτς = two sandwiches

In this sentence, if the meaning shown to the learner is sandwiches, that is perfectly possible. The Greek form itself does not clearly mark singular vs. plural here.

It means for the trip.

• για = for
• το ταξίδι = the trip

Here για shows purpose or intended use: the speaker is making the food for the trip.

Ταξίδι is a neuter singular noun, so its article is το.

So:

• το ταξίδι = the trip

Also, after για, Greek uses the accusative case, but with many neuter nouns like ταξίδι, the nominative and accusative look the same, so you still see το ταξίδι.

Here it joins the two food items:

• σαλάτα με τόνο
• σάντουιτς με γαλοπούλα

So the sentence is structured as:

[salad with tuna] and [sandwich(es) with turkey]

The second με helps make that clear.

For food, φτιάχνω is a very common verb meaning make or prepare.

It is especially natural for things like:

• salads
• sandwiches
• coffee
• dinner

Κάνω can mean do / make in some contexts, but φτιάχνω is usually the more natural choice when you are preparing something concrete, especially food.