Learn Portuguese (Portugal): Eles têm o que abastecer, por isso têm de abrir o minibar. - They have things to restock, so they have to open the minibar.

This sentence highlights the exact contrast your lesson covers. têm o que abastecer shows task possession: they have things that need restocking. têm de abrir expresses a pure obligation: they are required to open the minibar to get the job done.

What is the purpose of the o in têm o que abastecer?

The pronoun o translates roughly to 'that which' or 'the things that.' It makes it perfectly clear that they have physical items to restock. If you just said têm que abastecer, many Portuguese speakers would interpret it as a pure obligation ('they must restock') rather than possessing the items to be restocked, since ter que is often used informally as a synonym for ter de.

I often hear Portuguese people use ter que for obligations. Is têm de abrir strictly required here?

In strictly correct, normative European Portuguese, ter de is the standard way to express an obligation or necessity. In colloquial everyday speech, you will absolutely hear people say têm que abrir, but sticking to ter de is safer for formal writing and helps you keep the task vs. obligation distinction clear in your mind.

Is the verb abastecer only used for restocking small things like a minibar?