Word meaning "Automatic Gift"

There's complimentary:

[Merriam-Webster]
2 : given free as a courtesy or favor
    // complimentary tickets

In the example sentence:

Everyone receives a complimentary glass of wine upon entering.

As a corollary, if a gift cannot be refused (which I find unusual), it could be called obligatory:

[Merriam-Webster]
1 : binding in law or conscience
    // The ordinance made it obligatory that homeowners clear the snow from the sidewalks.
2 : relating to or enforcing an obligation
    // a writ obligatory
3 : MANDATORY, REQUIRED
    // obligatory military service
also : so commonplace as to be a convention, fashion, or cliché
    // the obligatory death scene in opera
    // The thriller included the obligatory chase scene.

However, an obligatory gift would normally be one that's expected to be provided, not one that couldn't be refused. However, even if the other sense is used, I think of no single word for "an automatic gift that cannot be refused."

How about swag. From Lexico:

swag: Products given away free, typically for promotional purposes.

Sometimes this is automatic (e.g., every attendee at a conference receives a logoed briefcase with items like program, paper, pens, refrigerator magnets, etc.), and sometimes it's not (e.g., attendees at trade shows can pick up all manner of free items at vendor booths).

Another possibility is party favor. From Lexico:

party favor: A gift, usually small and inexpensive, given to guests at a party.

This has the meaning of a single word and is automatic.