Food: European on Spring St. across from parliament; Madame Brussels around the corner (great rooftop bar); Cookies on Swanston (eclectic Thai restaurant with one of the best wine lists in the world); box lunch at Vue du Monde ($15 bargain at a restaurant that costs $500 for dinner); Ganache on Toorak Rd/Chapel St (great chocolate, better than Koko Black).
Bars: Martini bar at Westin (best mojito in Australia and beats any other Westin bar in the world); dozens of alleyway bars that are funky (e.g. drink from medical equipment), but I don't remember their names (the dangers of drinking). Hairy Canary (great snacks).
River walks: Yarra bend park. Actually I think you can go 20 miles along the Yarra, not just the downtown/Southbank part.