Using my bluetooth keyboard an my new iPad the other day I discovered there were many other keys available wen depressing the alt key. Checking on Macbook I see this is also the case with its keyboard.
So here are a couple of maps that show all these possibilities
The following layout is for the bluetooth keyboard. Note this is an OEM (Othere Equipment Manufacturer) type sometimes know as a CCC (Cheap Chinese Clone) and not the official Apple one. Works fine though. I believe it is US type layout as there is only a $ sign and no £ sign, but that can be typed by shift 3 as shown).