Are you packing your own lunch? Because all the places on campus will be closed on the weekend. I really can't recommend any of the surrounding restuarants as they are nothing special or you'll have to do some light climbing. How about eat somewhere in Balboa Island or on the newport peninsula?
Anyways, your instructions are spot on and the MUP should be clearly marked. You will be going on the San Diego Creek trail, not the Peter's Canyon trail. To get to UCI, take the San Diego Creek Trail to Campus Drive and head towards the campus.