Mayflower beach is routinely recognized as one of the most beautiful beaches in the U.S. - not just on the Cape. It may not be Tim's favorite (no surfing here...) but is very picturesque and has a decent snack bar where you could get yourself lunch.
Another great beach on the Nantucket sound side of Dennis, Corporation beach has a great snack bar where you could get lunch.
If you aren't interested in the beach, Main St. in Hyannis has lots of little shops, artist "shanties", coffee shops and restaurants. If you do go, we recommend coffee & a bit to each at Chez Antoine or for those with a larger appetite lunch at Anejo.
Chatham center is a very charming spot to visit with lots of places to shop, eat and spend an afternoon!