Hi! Since it's just a day trip and you'll be in Center City for the TUT exhibit I'm gonna stick with what's in walking distance. Let me know if you have a food preference and I'll see if I can find a good place for you.
Lunch: Good Dog has fantastic burgers and fries and all around yummy food, on 15th between Sansom and Walnut. Philly Falafel has duh, amazing falafel, on Sansom between 16th and 17th. Joy Tsin Lau has great Chinese food in Philly's own (little, tiny) Chinatown, on Race Street between 10th and 9th. Or you can go to the Reading Terminal Market for lunch. It's an indoor market with about four thousand or so different food stalls. There's a cheesesteak stand which is the third generation of on of the originals (I can't remember if it's Pat's or Gino's). The Market is on Arch between 10th and 11th.
Shopping: Walnut shopping (between 15th-20th) is lots of higher-end places with some mid-range places. Urban is here as well as Anthro. Also here is Knit-Wit which always gets written up in shopping guides and a couple other boutique type places. I actually like Sansom street for smaller places as well as any of the numbered streets between 15th and 20th. There is also South Street which has become very very commercialized and not so good in recent years as well as Olde City shopping (which is down on the lower one-digit numbered streets). I also like Pine Street between 12th and 10th for antique/vintage places. Are there any stores or places in particular?
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"But I want you to remember, I intend this breast satirically." Susan from Coupling