Toy Totes
Make up small totes with toys that are only brought out for special circumstances: going to a restaurant, when you are on the phone, in a waiting room, etc. Design a different tote for each circumstance. ONLY bring out the toys for the determined situations and occasionally switch out the toys so they stay interested.
Children tend to be at their worst when their parents are distracted or tense. Proactively creating a fun diversion for the children at these times can go a long way in reducing the added stress of a child in melt down mode.