If you ever need a giant calculator, or something more ordinary like blank CDs or printer cartridges, Unik Creations in Unity Plaza is a decent place. It’s not necessarily cheap – a huge calculator costs Rs. 1,500 and blank CDs cost around Rs. 25 each) – but it has basic office supplies you might need.
Other highlights, if you will, include printer cartridges, and the staff is quite polite. For more high end office needs you can check out The Fullstop, but Unik is not bad a mid-range sort of place.