You are by a lot of different things, 5-10 minute cab ride is going cover a majority of places for a day trip other than heading to the north of the island to go to the zoo.
I would check out Lau Pa Sat for some hawker fare. Chinese New Year is finally wrapping up and you could easily hop onto the MRT from raffles to Chinatown if you don't want to cab it...plenty of places to grab a bite to eat. If you are staying in Raffles area walk over to Chijmes one evening, plenty of bars and live bands if you are into that sort of scene. This is somewhat touristy but for a day trip I would consider one of the open top bus tours, do a quick one (no more than an hour).
I've been here for almost 9 months now and I honestly haven't had a bad meal. I live over in River Valley by Fort Canning Park so if you have any other questions let me know.
Fyi...be prepared for rain, we are getting rain almost daily this time of year.