I admit, I've never bought Toblerone except in an airport duty free shop!
Another option is to save them and sell them to a friend going to where you came from. We once ended up with over a thousand extra Australian dollars. (Long story that ended with my husband and me in a taxi to the airport, with my asking him "Where are you carrying the Australian cash?" and him replying, "Me carrying it? I thought you had it.") Anyway, when one of his co-workers went to Australia, we sold him our currency at the current exchange rate.
I don't worry about euros or pounds much, since I'm pretty sure I'll be back soon. But the currencies of Croatia, Poland, the Czech Republic, Hungary, etc--they're going to go the way of lira and francs in the future. Those I make a special effort to spend down.