Ginger ale mixed with grenadine or raspberry syrup is simple and good -- a variation on a Shirley Temple, which would also work (7-Up and grenadine).
Are you in a cold place, where hot drinks would be appropriate? A good "old-fashioned" milk-based hot chocolate is always popular (add egg and cinnamon for a Mexican version, or peppermint flavor for chocolate-mint). Or hot apple cider, with fresh cinnamon sticks and mulling spices.
A favorite when I was bartending was any fruit jiuce or combination of juices with 7-up or Sprite. Particularly good is Pineapple and Sprite or OJ, Pineapple and Sprite.
