I think there are a couple ways outside of official publications/presentations to demonstrate that you did quality research. It's difficult to say "creativity" in research, because that's difficult to measure. I'd like to present some more concrete ways that adcoms measure the research experience of applicants.
1) Degree of involvement. Measured by: LORs and stated at interview. If you have your own project or worked in a lab for awhile and earned your own project, this is ideal. You can also be assigned to a specific project, where while you are not exactly changing the directions, you understand those directions and you are not just cleaning bottles and making solutions for the person who is. Of course, quality lab experience is NOT just running gels, making solutions, and cleaning bottles.
2) Understanding of research. Measured by: mostly interview. Along with "Why MD/PhD?", this is the most important thing to know for your interview. Expect at many interviews an in-depth discussion of your research--the hows, the whys, the who else in your field, etc.
3) Potential in research. Measured by: LORs and interview. You need to show enthusiasm and of course your LORs have to shine in this regard. I can't stress how important interviews are for showing your potential AND as such, as a general indicator that can make or break your application. So many adcoms talk about those people who look great on paper, but are just so "white bread" (plain, uncompassionate), that they interview poorly.
Creativity is good if you're in the position to be creative. That is, you are in something that allows for great flexibility and you are leading your own project. This doesn't happen for everyone, and this is understood as well.