Learn Hardcore Polish: Pamiętaj, żeby wziąć torbę na zakupy.

In Polish, you usually place a comma before subordinating conjunctions like żeby when they introduce a subordinate clause. Here Pamiętaj is the main clause and żeby wziąć torbę na zakupy is the subordinate clause expressing what you should remember.

What does żeby do in this sentence, and can I replace it with aby?

żeby is a subordinating conjunction introducing a purpose/intent clause (“remember to do X”). You can indeed replace it with aby:
• Pamiętaj, żeby wziąć torbę na zakupy. (colloquial)
• Pamiętaj, aby wziąć torbę na zakupy. (slightly more formal)

Why is the verb wziąć in the infinitive? Why not the imperative weź?

The structure “remember to do something” in Polish requires pamiętaj + (żeby/aby) + infinitive. If you use the imperative directly, you get a different sentence:
• Weź torbę na zakupy! (“Take the bag for shopping!”) – a direct command.
• Pamiętaj, żeby wziąć torbę na zakupy. (“Remember to take a bag for shopping.”) – a reminder.

Why is torbę in the accusative case?

torba is the direct object of the verb wziąć (“to take”). In Polish, direct objects of transitive verbs appear in the accusative case, so torba changes to torbę.

What does na zakupy mean, and why is zakupy plural?

na zakupy means “for shopping” or “for groceries.” In Polish, the noun zakupy (“purchases,” “shopping”) is typically used in the plural when referring to the activity of shopping:
• Idę na zakupy. – “I’m going shopping.”
Here it specifies what the bag is for: na zakupy.

Can I drop żeby and say Pamiętaj wziąć torbę na zakupy?

No, in standard Polish you need żeby (or aby) to link pamiętaj with the infinitive wziąć. Omitting it makes the sentence ungrammatical or at least colloquially awkward.

Could I use nie zapomnij instead of pamiętaj?

Yes. Nie zapomnij wziąć torby na zakupy has essentially the same meaning (“Don’t forget to take a shopping bag”). Nie zapomnij is a negative command, while pamiętaj is a positive imperative, but both work to remind someone.

Is there a difference between wziąć and zabrać here?

They are close synonyms (“to take,” “to bring along”). wziąć is neutral and very common for “take something with you.” zabrać can imply removing something from a place. For packing your own bag, wziąć torbę is the natural choice.