If you want to eat something on campus check out Pappy's Sweet Shop in the Memorial Union (aka the Union).
http://www.hotel.purdue.edu/DiningPappysSweetShop.html
There are also a few other places in the Union.
You may also want to check out Triple XXX.
http://www.triplexxxfamilyrestaurant.com/index.html
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I just ate at a place last week called "McGraws Steak Chops & Fish House."
http://cityguide.jconline.com/fe/Din...sinessid=29661
It's a local place just south-west of campus that tends to have nicer food (yet more expensive menu $$). I just went there for a birthday dinner with my family for the first time and we all enjoyed it. Most people wear nicer attire when visiting, but I felt fine in a hooded sweatshirt and jeans.
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EDIT: Like Kyle said Arnis is also a great place to eat. It's mostly a pizza place, but they do have other items.
http://www.lafayette-online.com/arnis/