So what do you do when you have a hankering for really good lox and bagels and you live 3,000 miles west of Amsterdam and 86th? Make the trek to upper Polk Street, where a six-block jaunt between establishments will yield a brunch well worth the Muni fare. Start at Swan Oyster Depot, where the gregarious countermen will fillet and slice the creamiest, butteriest smoked salmon in the city before your very eyes. Next, hoof it on up to the Bagelry, home of the Bay Area's best bagels, for a bag of their chewy, substantial delights in egg, onion, or poppy seed. Then dash across the street to Real Foods for your banquet's indispensable final accents: a jar of capers, a sweetly pungent purple onion, a cluster of juicy, luscious vine-ripened tomatoes, and, of course, plenty of puckery cream cheese fresh from the Straus Organic Dairy. Note: Since Swan isn't open Sundays, this brunch-ish maneuver has to be executed by 5:30 p.m. Saturday.