There are two basic types of items you can get your dad for Father's Day, ones for use and ones for decoration.
Gifts intended for use are the most sought after and getting one that your dad will use on a regular occasion is one of the best gifts you can give. But this is not easy to do. It might help to start out by asking yourself what you dad will use. This is done easily by thinking about what he already uses. If he already uses the product, then you know for a fact that he will use your gift. Some ideas can be soaps, creams, hair products, socks, clothes, shoes, ties, and more. Some gifts that he might not already use commonly but still might be interested in would be cufflinks, tie bars, wallets, money clips, etc.
Although these types of gifts are not as common in terms of a winner gift, they are still appreciated and used commonly. Gifts for decoration can be things like art or bottle openers. Things like bottle openers can also be used in addition to just being used for decoration. Make sure that when purchasing a gift from this category you make sure that your dad will appreciate whatever it is that is being used for decoration.