You’re in the clear to buy off the registry…if it’s there it’s free game.
That said, you still have to keep value in the equation…not just for your own budget but also for receivers.
For example, if your overall financial situation is pretty reasonable and the wedding party itself is more traditional in terms of venue, catering, etc., you may need to consider if that $11 scoop is appropriate as a standalone gift. I always use cash as a default position but if I do decide to go from the registry then I try to make sure that the cost of the gift(s) I give are about equal to the amount of cash I would have given.
So, if you would be OK with giving $11 in cash as a gift, then by all means go ahead and give the scoop.
If nothing is left on the registry that fits within your budget just give cash. I actually think that most newlyweds nowadays would actually prefer it…
Re: gift cards — why bother unless you’re really keen to introduce the couple to a store/experience they may not know yet or you’re absolutely certain that it’s something they want to use? Just give cash or check…it’s easier and more universal.