This is very much dependent on the person you're buying for. However, it's important to know their favorite characters. Just because something is Animal Crossing related, it doesn't mean that the person will necessarily like it. For example, if you gifted me something themed around Ketchup or Merengue, then I'd be thrilled, but if I received some merch with Leopold or Rolf on then, I'd give it away at the first chance I got. Try to ask the person which characters they like, but if you don't want to give away the surprise, then go for something more generic like an icon print or the leaf logo. As for which item to get, I think you can never go wrong with something wearable like a t-shirt or socks.