May be some game streaming with card giveaways for ppl who watching ?

Well, i have a pretty simple suggestion: Just do a trivia competition with a question every 5 minutes and then after a certain number of questions, you close the competition and announce the winner. This should encourage more people to stay alert and check the group often. You can do this at regular times every day until your cards run out.

Something sort of "pay it forward" will do fine. But it takes a lot of personal responsibility or strong moderating.

The idea is simple.
Each participant may eneter a competition and then random person wins. The ones, who win a card, then create a giveaway of their own.

The other, more wacky and hardcore version - the ones, wno DON'T get a card create a giveaway.:)

I think people that posts trading threads really want change and get new cards and badges. The same I'm thinking about people that answer under a thread. So, make a list. Take there about 7 of first threads creators. Then look in that threads and take randomly about 5 people that posted a reply. Then you have 7+7*5 = 42 people in your list. After that just choose randomly few winners (or more) (for example: random.org). Not very hard, isn't?

I could have an idea too:
For some of the card giveaways, you can give a little "task". For example, the ones, who want to participate, must answer a question, or the people must write a joke, a history with fun, a recommendation for a game, or even posting an opening of an anime or a show... There are many possibilities, but the main idea is "doing a task".
For this idea, you can easily use your creativity.
If you find, that the task is done, you can choose one or two or five winners.
If there are too many winners (in your opinion), they can do another task to get another chance. But generally, this is only an idea...

I like Shadow-Guardian's idea of "doing a task," but make it more of a challenge. Write a haiku pertaining to chocolate-covered bacon, re-write the Gilligan's Island theme to make it about XCOM, come up with a short parallel-universe story for that poor potato from Portal 2, etc.

Promotes creativity and it'll be hilarious to read.

It would be funny to see contests where you have to respond to a hypothetical question or tell how you would have done in a cetain situation of a game.

Examples:

• [Portal 2] If GLadOS was Mr. Cave Secretary, who was Wheatley? And the Adventure Core?
  
• If you were a developer, which games would you like to make a crossover with?

And the winner doesn't have to be the most original respond. It can be the shortest, the funniest, the craziest, the most complicated, the most ridiculous, etc depending on what you want.

Examples:

• [use someone famous] I don't know about them, but I'm batman.
  
• [impossible] COD + FIFA, that match would last forever.

Maybe a rebus type of thing, which involve questions about the booster pack games. Each answer would correspond to a word or part of a whole sentence. This sentence could say what to write in the comments to win or enter the giveaway. Might want to hold off on spoilers though.

As an extra, the order of the words could be another puzzle.

You could also have just a collection of words and the task is to make a guess for another game with the words as clues.

I like the idea of CaboGuataca. That can be very hilarious. But it would be also nice to have a week, where everybody is sending questions (without answers of course) and the best are will get some cards.

Weekly raffle where we pay a card to enter into a chance at a random set. Hopefully, there will be enough people entering that there should be more cards coming in then going out, making the next raffle possible. On top of that, should you be making enough cards, you can do free raffles whenever a surplus of cards exists.

There might be a few things that need a little bit of changing, but this is the base.

Maybe some sort of weekly trivia?
(:

maybe some kind of chat-games?

to hell with trivia. Do one based on saltybet! ( http://www.saltybet.com/ )