Hi there @ramsa1976
the giffgaff app uses an internet connection so yes, you will need to have some form of connection to the internet to top up your account using the giffgaff app/website. It doesn't have to be data, wifi will do.
I am assuming that you have an internet connection to post on this forum?
If you have no way of connecting to the internet then you can dial 43430 to top up too. I recommend using the website instead though
That's what I meant even though you'd run out of data you could still access giffgaff. I did this plenty of times in the past. I ran out last night at midnight hence no shops open to buy voucher.
You can access the giffgaff website with no goodybag or credit. The phone that I'm posting this from has no credit or goodybag. However, it's VERY SLOW - its taken over half an hour for me to log in and navigate straight to this thread!
Still, it should be possible to buy a goodybag this way.