I often have a little notepad & pen around my potting bench (an old washtub) for lists like that, but those little pads tend to be migratory... A magnetic dry erase board would probably be more obedient!
I want to know, though, what is a gazinnia?? It sounds quite special. I think you made it up! (But just in case you didn't, I need to know about a plant that made your white board list!)