Although you're welcome to do whatever you like, I would not recommend drawing whatever people suggest for you here. I would instead come up with your own ideas that you know will show off your level of knowledge with basic art fundamentals. You need to either find something you've already drawn that shows your best ability in those important skill sets or make something new that will do that for you.
The theme or subject of an artwork is probably one of the least important aspects in a portfolio. The things that do matter are your use of color, composition, anatomy, value, line, texture, and form. If you can show you're comfortable using a particular piece of art software or medium that you know will come in handy at the school, that's a bonus as well. Probably one of the most useful things you should consider putting in your portfolio is some sort of life drawing(s) - preferably of humans, but still lifes can be useful too. Go people-watching and draw the people you see, or get someone to pose for you. Even simple abstract art pieces can say a lot about your skills.
You could still record your progress if that helps motivate you, but your goal should be to fill your portfolio with work you can be proud of, not working to please anyone around here. Because (and I hope you don't mind me being totally honest here) if you can't find a way to motivate yourself to just get the acceptance portfolio done, you're probably going to find yourself struggling a lot later on when you get to the actual schoolwork.
Again - you're welcome to do whatever you want. I have no idea how strict the acceptance is for the school you're applying to, so it might not even matter. Just trying to offer advice if you want it.