You can buy Ned anything you want. If you buy him something lame, he'll be sweet about it, but he and Nancy will laugh about her bad taste. If you get him the right item, however, he'll be ecstatic.
So let me think. If I were a man, what one item in this gift shop would make my pulse race?
Oh, come on, the sword, what else? Of course, it is the most expensive thing in the shop ... but honestly, isn't Ned worth it? And doesn't Nancy have a lot to make up for?
All the same, you can give him a postcard or a candy bar, or nothing at all, if you'd rather. It's up to you.