Magazine Mood Board
Gather a bunch of different magazines with lots of pictures. (Note that new magazines are quite expensive these days, so if cost is a concern, see if you can scrounge some used ones.)
Cut out anything and everything that relates to your theme.
Collage them together.
Note: If your pictures are small, feel free to use a page in your Project Quartz journal, but if they’re large (or you found a lot of inspiration!) consider upsizing to poster board or even a wall.
Source
Melissa made a magazine mood board for Project Quartz, which still hangs in our office to this day.