Cleaning chemicals
Concentrated cleaners decanted into unlabelled bottles, mixing products (bleach + acid = chlorine gas), splash exposure, storage next to food or within customer reach. The never-mix rule isn't caution for its own sake. Bleach with an acid (many toilet and tile cleaners) gives off chlorine gas; bleach with ammonia (some glass cleaners) gives off chloramine. Both are toxic, both land people in hospital, and people have died from it in ordinary cleaning cupboards — usually because they had no idea the two bottles reacted. That's why decants get labelled and products stay in their own containers: so no one combines them by accident.
This is one hazard. Your register is the set that applies to you — under 20 questions, about five minutes, free.