It depends on what you want to put in there.
In the past we used to put a load of tat from the likes of Hawkins Bazaar, which goes the way of party bag crap.
But more recently, I have bought real presents to put in there. One year I bought a load from John Lewis on line. The items were lovely, and were all used, rather than being crushed underfoot within a month.
So, what about some small books, some Lego mini figures, a DS game (or the like) some costume jewellery, a whoopi cushion, some stickers, some biscuit cutters or silicone cake moulds, a DVD, a purse, some bubble bath (the department stores all do little bottles).
I know some of these are more expensive, but if they would get them anyway, it's just another way of them receiving the same present. In our family, we give the big things, and FC gives the stocking!