Ties
The chance of you actually finding a tie that (a) your dad doesn’t already have an exact clone of and (b) that your dad will actually wear is around 0.1%. Unless you go with a novelty tie, which you will think is a hilarious and great idea, but is almost guaranteed to be greeted with a forced, “Oh, thanks, that’s a funny tie.” Plus, ties are surprisingly expensive. There are much better routes to take.