adverb
present, with it
A2
Means 'present' (e.g. ich bin dabei = I’m there/participating) and 'with it' or 'along with that' (e.g. etwas dabei haben = to have something with you). It's an adverb, appears in set phrases like 'dabei sein' and doesn't require a preposition.
Examples
Ich habe das Rezept und die Liste dabei.
I have it with me (I brought it).
Sie war nicht zu Hause, aber beim Treffen trotzdem dabei.
She wasn't at home, but she was still present at the meeting.
Die Kollegen trafen sich zum Mittagessen, wobei Maria nicht dabei war, weil sie krank blieb.
The colleagues met for lunch, with Maria not being there because she remained ill.
Details
Mnemonics
Picture being 'there by' someone (da-by) so you are present.
Sounds like 'da buy' — imagine buying something there and being present.