You list the authors in the order they are listed on the abstract, whether it's a publication or a poster/presentation. You can always add parentheses after the citation stating what your role was (poster, presenter, etc.). Most meetings make the first author present, but if you presented something you're 2nd author on, you list your name second.
Also, keep in mind that if you presented a paper at a meeting, you can list the citation twice on your ERAS -- one for the presentation, another for the publication.
