It's an almost constant feature of the help forums to have at least one or two posts from a new member who's topped up thinking that would give them a goodybag, who then find they'd used 5p or £1 credit and need to top up again to get the goodybag. We've all read them.
So, how about during the top up process, adding another page to give people the very clear option to convert the top up straight to a goodybag. Like this -
Option 2 and 3 would link through to the goodybag buying process.
Of course, I know there's the goodybag page where you can do all that, but obviously some new members are getting confused. This would hopefully alleviate the problem somewhat. After all, the goodybag page lets you buy credit too, why not the other way round?