So what's a relic? Again traditionally There are three classes of relics: the first, is a literal -part- of the figure of significance, –hair, limb, bones.
Second, items that were directly involved with your figures story, think of it as accessories.
The third is anything touched by your chosen figure. All then made precious by encasement
So first you need to choice someone or something. Perhaps you already have with your Icon? Think of the Icon as an image of something or someone and the Reliquary as a physical piece of something and/or someone in a fancy case, a sculpture.
Now remember we are here to get our creative juices flowing, so if you feeling religious go for it and if your feeling sacrilegious go for it as well. Or maybe your feeling like remembering someone or something long gone, sounds great. But maybe you just want to have fun, we always welcome the humor. I personally I'm thinking about a lost childhood toy...if only I had a relic of him.