Hi nikki76, more than likely once your sim is fully activated. When you go into your My giffgaff at the top, can you see a live telephone number and balance? If no, please wait for this to show up first. If you can see this, try logging out, closing and re-opening your browser and log back in and see if you get the option then.
Buying a goodybag is broken at the moment, check back later! hope this helps