If you're going to be playing at a pokemon league, then you're going to need cards from the current format to build a deck (Black and White through the current set). Any cards printed before the B&W set are considered illegal for tournament play (except for energies and certain trainers that have been reprinted in the recent sets)
So you might want to pick up a few recent packs to add to your collection. I would recommend B&W Boundaries Crossed as it has some good cards for decks.
And if they have these in your area, you could buy the new EX tins that have Darkrai EX, Mewtwo EX, or Rayquaza EX as tin promos (I would recommend buying a mewtwo EX tin) Mewtwo EX is used in alot of good decks.
Hope this helps