I've forgot to pack a kayak paddle a few times..
One morning I loaded the yak ontop of my car for a quickie before work and for some reason I felt like I was forgetting something..made it down my neighborhood road (25 mph limit) before turning out onto the main road (50 mph) and decided to pull over to check everything over and it turns out I forgot to ratchet down my kayak (straps still in the trunk). Glad I caught that one.