Where, oh where, can I indulge a Snack Attack in the charmless wasteland of Madison Avenue? My friend Lydie and her husband Chris are experienced urban hikers, so I trusted the tip Lydie texted me one afternoon during their Sunday stroll. “Sant Ambroeus on E. 61, sandwiches for $5.50.” She sent a beauty shot of a small pressed Panini with a frittata and tomato spilling out of the edges, two dainty cookies, and a foamy coffee drink.