Avoid salt

Snack foods give you a sodium overload, which is especially bad before a meal. Cheese biscuits, crisps, peanuts and the like are absolutely loaded with the stuff, which means you end up overdosing big time and eating and drinking more as a result. 

Not only is salt bad for your health (it contributes to high blood pressure): it also causes water retention and increases appetite. Avoid anything too salty if you can.