USS for the entire day, and drop by Sentosa if you have the time. You could take the tram/cable car to vivocity and have dinner there after everything. Vivocity is a huge shopping mall which has a lot of restaurants, so take your pick. OR, if you are more keen on hawker centre food, there's a hawker centre across the bridge from Harbourfront Centre which is right next to Vivocity. Just ask around, the locals will be able to lead you there.