@Bakersdozen - Congratulations on the upcoming birthday. My mother is a great fan of entertaining and every season seems to bring an excuse for a holiday cocktail party.
The food she serves is generally quite plain. Think of things that won't drip or fall apart. Most guests are reluctant to lose their drink, so you need things which can be eaten with one hand.
Think small bite size pieces of bread based snacks crackers with a soft topping or small shrimp on a little stick. One bite tartlets are always popular too.