Gentlemen, got problems with this? No worries, i am here to help everyone.
To pick up the killstreaks, you have to first enter the console (if you don't know how to get the console in-game, then go check a guide on how to) and type "bind (insert key here) use_killstreak" WITHOUT the quotes. Once you get a killstreak, press the key you bound to obtain it. Now, the killstreak won't activate itself: once you press the button, you will obtain it as a SWEP. Cycle through your weapons to find it. Once you found it, take it out AND, depending on the killstreak you get, DON'T CLICK ANYTHING while it activates (unless it's a Care Package: you will get a smoke grenade and you have to throw it somewhere to call in the helicopter).
About bugs:
Bug #1: Killstreak Package not working.
Sometimes when you will try to obtain the Packages by pressing E on them, they will not work. That is cause of some hitbox bug that does not let you use the package from certain angles. To make it work right, you have to first correct its position with the Physgun (if necessary) and then open them on the front like you would do with a normal box in real life.
Bug #2: Care Package Helicopters going through the map.
Reason? Pretty easy to tell: the maps where you play must be AT LEAST bigger than gm_construct.
Bug #3: Invisible Stealth Bomber.
Well, you can't do anything about it. That is a bug Braintwistah was working on, but did not fix, so nothing to do about it (unless someone gets to fix everything, then i will order 10000 trucks of medals for that guy).
Bug #4: Sentry Guns cannot be picked up again once planted.
It means you are too far away from the Sentry to pick it up. You have to go as closer as you can, like you would in real life picking an object with your hands and putting it somewhere else.