Portfolios are a good mechanism of demonstrating your skills and activities in a format that is much more extensive than a resume. 

Here are examples of some portfolios that current and recent students have made.  (I want to feature more, so please let me know if you are willing to have me do so):

Gregory Hewett - EE (2017)

Vincent Chow - BioE (2016)

Simon Shuham ME (2017)

Brandon Hopkins ES (2011)

Most of these students used commercial websites, like Square.  However, there is also a free alternative that is open to Harvard students - openscholar.harvard.edu