How about giving out beautifully decorated cupcakes in individual boxes in place of party bags! Blue ones for boys and pink ones for girls, or what ever you would like to go with the theme of your party. I know my 11 year old daughter would love these as gifts for her party.
These would be a great price of £2.50 each, no more than you would spend on party bags but with the added wow factor!
I will add pictures to the site this week of examples