Question for people with Diabetes(Types 1 and 2)?

I work for a company that does not allow patrons to bring their own food or drinks inside our building. However we do allow small amounts for special needs customers (like people with diabetes.) But everyone that brings food claims they have it and I know some of them are lying. My question is what types of snacks would someone that actually has diabetes keep with them in case their blood sugar drops? Because many people come in with burgers, fries, and soda and claim they need it for emergencies. Anyone care to give some examples of what you like to carry around with you?