Illustration portfolio

Hi guys,

Basically, Ive got a few interviews at unis to study illustration, and obviously I've got to take a portfolio but I am so confused on what to include in it! They say they want 10 - 20 pieces but I just confused of what to include. So far I've included still life drawings, large-scale paintings, digital illustrations.. I'm stressing myself out as I clearly want them to like my work and to get a place. Can anyone help me out! Would be great if I could see some portfolios! Thanks!