resume building

In Sept. I have been invited to a national conference for addiction treatment professionals. I have been invited to do two things, first a co-presentation on ethics in small communities and second a poster presentation on auricular acupuncture and it use in addictions treatment. The ethics presentation in on a Saturday but the poster session in on a Tuesday. I would have to miss two days of classes in order to do both. My question is: is it work missing two days of classes to do a poster presentation? How much of an advantage will having this on my resume be when I go to apply for medical school next year?