The kid in me thinks that all this stuff would be fun to have. I was looking through the $10 "boy toys" and just saw a lot of great items that were $20 or more and dropped into the under $10. Even if it does say for boys, I know an 8 year old girl who would love this stuff.
Buy a few good spy tools here:
Add in one of the Spy Kids movies (or these three for $12.49):
Then add in some good mystery books. What an awesome theme.