If i get 3 kills with out getting killed and pick up the 3 dog tags to get the radar if i then use the radar. Do i only need to get 2 more dog tags (without getting killed) to make up the 5 for next item or do i have to get the 5 again because i already used 3 for the radar.

You just need 2 more, its cumulative per life.

And when you get 3 dog tags and you get the rader, even if you die and have not used the radar it remains. But of course you'll have 0 Dog tags again.

Cheers ,ye that was my next question do they carry over to next life you ruined my next question lol cheers

You're welcome, I enjoy ruining questions