Can data be accessed on a lost iPhone that was reported to "find my iPhone" My phone was lost today, I tracked it (someone had it).  

I reported it LOST with "find my iphone"and suspended my service.  

Can someone activate it and use my apps, itunes, passbook, etc?
It depends. 

If you are on iOS 6, they can wipe the device and most likely establish new wireless service even in the same country as you reports it as stolen. 

If you are on iOS 7, the activation lock from iCloud and Apple is a very hard thing for someone to bypass - perhaps impossible for most to use again.