I am going to whisper very softly here on where to park. You can park at the Dryden Road Garage in Collegetown. You can walk to the stadium from there, even though it can be a bit of a hike for grandparents.
Bring a light color umbrella and a plastic raincoat. The umbrella is for the sun before the ceremony (they ask you to take down your umbrella when the ceremony starts), and plastic raincoat in case of rain.
This will be our 4th Cornell graduation (it’s for my nephew). You need to make restaurant reservations very early on. I booked a lakeside house for both of my kids’ graduation a year ahead. My brother didn’t believe me, so we stayed at a worst hotel in Ithaca when my first nephew graduated. This time around they booked a house a year ahead.