Sitting on the bus/in the park; in fact, anywhere at all, a plot could be looming above you; or lurking behind you, waiting to strike. The perfect title or character flashes in and then zips out again just as quickly and you must be ready for it. This could be your big chance: the idea that makes your fortune (or your name; whichever is your dream) don't lose it, grab it – write it down.
As any writer knows when you start to create stories all of a sudden you find yourself drawn to strange and interesting people and places; things just happen to you almost as if you are being tested; can you turn this bizarre set of circumstances into something anyone would want to read?
Events, signs, conversations are firing at you – a Kalashnikov of material, just for you.
Make a plan to harness whatever appears; perhaps categorise: names, plots, titles, twists, endings. Oh, there's so much of it. But just think, if you keep the information safe, when you do a search on: dog in a wetsuit found in a duck pond with an oxygen tank full of bonds strapped to its back, there it is ready and waiting for you to incorporate into your new novel.
Write it down!