I've seen every kind of Killstreak reward from the UAV to the EMP but NOT the tactical nuke. You can also get ammo which just does much the same as picking up ammo packs using the Scavenger perk.
Mostly you have a high chance of getting low value killstreaks that are easy to earn but have a lower chance of recieving high value killstreaks which are very difficult to obtain before being killed and then having to start again. Some people prefer to have a killstreak setup consisting of the UAV/Spy Plane, Care Package and another killstreak after that in case they get lucky and manage to kill more people. MW2 and Black Ops allows you to get ammo from Care Packages while MW3 doesn't but instead allows you to use another variant of the Care Package which is an explosive trap disguised as a high value killstreak such as a Juggernaut or Assault Drone etc.