A few days ago I gave my little tray more pajazz by just adding patterned paper and a piece of glass.
|Tray / Glass / Patterned Paper / Craft Knife / Self-Healing Mat|
You can use any paper that you like; pretty wrapping paper, scrapbook paper, a child's drawing, anything. I used a piece of wrapping paper from our local paper shop.
Once you have all the material, just cut your paper to fit inside your tray. Simply place the cut glass on top of your paper and cut around the glass with a craft knife. PLEASE make sure to cut on top of a self-healing mat of some kind. You will ruin your table or floor if you don't.