Although you want your portfolio to be built with simple organization in mind, you also need to be able to fit everything you need inside without struggle. Depending on your needs, this could mean a few business cards, a notepad, and some sheets of loose paper, some covering letter.
You might, on the other hand, require the portfolio has space for your smartphone, tablet, or more than one pen. Either way, it’s best to go with something that will fit more than you think just in case. At the same time, you should ensure that it comfortably fits into your briefcase for portability. Sometimes,you can choose a leather portfolio with handle which it's more portable than carrying another briefcase to hold it.
Using a leather portfolio, in the first place, is meant to help you come across as prepared and professional, so make sure you choose one that looks nice with enough space.