What's afternoon tea without 'tea cakes?' A quick way to present some tea cakes at the last minute is to simply slice mini cupcakes or muffins in half, then top with some whipped cream or frosting. See the pic below.
Or you can buy some mini tea cakes and pastries at a bakery.
Mini sandwiches are also another option. Just make sandwiches of cheeses, smoked salmon, and/or various spreads. Even create a few vegan ones using thinly sliced cucumber, mashed avocado, sliced tomatoes and fresh basil. Cut sandwiches in quarters. Or use a cookie cutter for different shapes. Add thinly sliced cucumber, radish and some watercress
Here is a fun link for more recipes and info: http://britishfood.about.com/od/AfternoonTea/ss/Afternoon-Tea-Recipes.htm