Throw me a little more details..? I'm probably going to skip the bar to bar aspect. There's a fair chance I'll loose track of time and end up being cained for public urination.
Orchard Rd has the usual shops and stalls along it at ground level but the shops also link underground mostly and there are lots and lots of little street food vendors. You can also head upstairs in the shopping malls but my favourite part is the street food. I have been able to sample some amazing flavours and the beauty is you can just buy bits and pieces as you wander around.
At Marina Bay ths shops are (in my experience) very expensive so it is just a walk around and time wasting exercise. The museum quite often has great displays on. One time I was there it was about band camp... ummm actually the Chinese fleets of the early 15th century, I spent a couple of hours there and learnt a lot, so much that I followed it up with some other research when I arrived home. Sometimes it is less interesting. You can get a day pass onto the roof of the hotel and there are a couple of restaurants up there which are free access. I was a bit disappointed to be honest. Crazy expensive and not the culinary experience I expected. The new forest is the public development on the ocean side of the marina with some of the artifical trees being accessable. The trees are water towers and processing for the city water supply. Great at night but you maybe wont have time.
I don't seafood since it would put me in hospital but you can get a taxi from the airport to the wharf area and indulge in chilli crab which is amazing. Alledgely though I have had the sauce on another dead animal and it was pretty special.
There is also the four floors of whores. I am pretty sure that poodles aren't allowed.
Just watch your time. If you are going into the city/Marina Bay use the mrt not taxis. Taxis are cheap but one visit I spent my 4 hours in transit because it was Singapore cup time and the roads were shocking. I did not know or check.