Lots of great restaurants in Portsmouth. For casual sandwiches, soups, wraps try Popovers. If it's nice out you can eat outside. For something a little less casual (Popovers you order at the counter and pick up your own food), try the Portsmouth Brewery or the Riverhouse.
If the weather is nice, just walking downtown or visiting Prescott Park is always nice. There is outlet shopping over the bridge in Kittery.
Hope that helps, have a great time!