I'm one of those who generally don't like cycling with backpacks although a small hydration pack (enough for up to 3L water plus a seat pack worth of extra stuff) is sometimes acceptable. However, for day trips and overnighters where I would need more space, I'd go with a rack pack, the new bikepacking saddle or handlebar packs or a small set of traditional touring bags (ok, maybe the last for an overnighter, not a day trip). Futhermore, Singapore, I understand can be hot and humid, I'd rather have nothing on my back in those conditions.