Probably just about everything.
The shops in Singapore have to pay shipping+make a profit, so things are more expensive here. The US shops have to make a profit, no need pay for shipping.
That being said, we don't know your preference (say a Gretsch vs a Jackson, and you're looking at modulations, drives...)
If your friend's at Guitar Center, i'd say a Fender Black Top is getting, it looks like a good deal. For acoustics get a Breedlove.
For pedals, a Moog delay if you can afford it, you hardly see any in Singapore. Also a Hughes and Kettner drive, i don't think they are any dealers locally. There's also this new Diaz Texas Ranger treble booster, looks good. Seems like most other stuff on their website, like MXR, Boss, Danelectro, Morley, etc you can get for decent prices here.