What can I put in my daughter's lunchbox to take the place of a cookie or muesli bar?

She packs her own lunch - a sandwich (yes, I know it's not primal but I'm not worried about that at the moment), piece of fruit, handful of nuts and one more thing.

I'd like it to be something regarded as a treat, since her friends would probably have a muesli bar or pkt of chips etc. Sometimes she has a primal truffle ball or piece of ricebubble slice, but I need some more ideas. It's a shame that straight chocolate is probably not acceptable by school rules (no lollies) as it would be so easy and good.