My EDC FAK (ie everyday carry first aid kit) is a small plastic band aid box. Maybe 3x3x1 inch. After a few months I realized what gets used the most is not the bandaids but the Pepcid and chewable Pepto. Now i put in a couple Tylenol and a couple Immodiums, couple Benadryls for allergy sufferers which can be as debilitating as any major wound. Plus ya know, couple bandaids.

It's a day trip in the city. Other than being out of your natural surroundings, what you carry on you shouldn't be all that different than what you carry on you every day for work.

As what others have mentioned toss in a book. Maybe a small radio or smartphone app that lets you listen to your stations back home. Hat. Some jerky or powerbars since you know you'll gone the whole day. But campuses are pretty good about having hot food available healthy or otherwise. extra cash.