Glad I could help.
does anyone know if there is a way to trade cards if you have all of them?
Can someone explain this to me? WHat exactly do characters and strike/support package do? How can I unlock characters? This isn't Gears of War. Also, does the killstreak stuff let you unlock them early or something?
Are you talking about the Combat Cards? The cards on their own do not do anything other than offer you small tid-bits of information. If you collect a whole set (one of the three rows of five Combat Cards) you will receive a bonus 15 minutes of double XP. If you complete all three sets you receive a bonus 45 minutes of double XP.
And what about Gears of War?