I often use the Notes on my iPhone for lists of information - books to read, movies to see, and things to buy. Did you know you can add a photo to your notes?
A client shared this helpful tip: when she creates a list of things she'd like to buy for her home, such as new kitchen stools or a rug for her living room, she snaps a photo of the space and saves it with the note. Then when she's out shopping not only does she have the note about what she needs, she has the photo of the space also. This visual is a great reminder for wall color, scale, and other patterns in a room.
You can also add sketches to notes! If you are not sure how to do it, here's a great tutorial to get you started.