I usually don't give a gift on the registery. Everyone else will do that. I usually get something that's extra.
A nice carving set is a favorite wedding gift for me to give. But, then again, I like the pagentry of carving at the table.
A set of fine chop sticks is another. Everyone always comments, "Wow. We never thought about having 'good' chop sticks. That's great!" (But, then again, many Americans aren't familiar with chop sticks that you don't have to break apart before using

)
A set of crystal martini glasses and a very classy shaker are another item that will class up the newlywed's new home.
A really good cork screw is a good wedding gift. Not one of these fancy gimic things that abound these days, but just a really good stainless-steel cork screw that will last a lifetime. They are a pleasure to use and the bride and groom will think of you with each bottle they enjoy for the rest of their lives.
If you want to go practical, get them a really nice, heavy-duty, 3-wire, 100-foot extension cord on a really good reel thing. They'll use it for years and years and years and thank you each time.
You need to be a bit careful giving knives for wedding gifts. In some cultures, especially some Asian cultures, knives at weddings, even as gifts, are seen as bad luck or a sign of malice. In the case immediately in question, where the bride and groom registered for a knife set, it's clearly ok. But, it's just something to keep in mind in other cases.