Oh I’ve been single for years and I give bad advice so I don’t really…know…probably something that reflects an interest of theirs/their sense of humor? You can usually find cute or small things relevant to specific niche interests on like…Etsy. Like if your SO has a favorite piece of art, you can probably find a phone case cover that has it. 

Favorite book among the last like…twenty I read would probably be Faithful by Alice Hoffman.