I am submitting an abstract for a conference that, if accepted, will be published in its "book of abstracts". I know that wouldn't cause any issues for submitting the paper to a journal, but I'm wondering whether I can actually copy and paste the sentences that I'm using for the abstract in the journal draft, or I have to rephrase them. Is it self-plagiarism? (The field is NOT CS, so the conference is worth very little, and probably after publication only the journal paper could receive some attention.)
I reviewed the answers to these three questions, but I couldn't find the answer to my question. Only this answer says "I'd avoid the same wording", but it's not clear whether that's just optional or could be as serious as avoiding plagiarism.
(Note: The conference's book of abstracts will be published quite a while before the journal paper, and probably even before submitting the journal paper.)