What do you mean by "major publication". I don't think programs reviewing your application look at your research experiences at categorize it as major publication or not. The best is to have first author original scientific manuscript (clinical vs basic science probably doesn't matter, the impact and implications of the research do though). Publishing in Radiology obviously looks better then some random journal, and from what I've heard most people don't care about papers you're on if its beyond second author. Lots of people could care less about a case reports, and abstracts are kind of a dime a dozen for applicants (I didn't even include all of mine on ERAS), although if they lead to oral presentations they do look good.
If you're preparing yourself to apply, try finding projects that have a high likelihood of being published, such as one where negative or positive results would be interesting. Also, to play it on the safe side I wouldn't expect a paper you've submitted to be officially published until around 6 months afterwards. So try getting in as much stuff as you can early.