NIS America is going to save you Disgaea superfans a little time, by allowing you to buyDisgaea 4 and a tie-in toy at the same time. The publisher announced a Premium Edition, which will be available at "GameStop and other retailers" at the September launch, and contains an artbook and an exclusive Nendoroid figurine of Fuka (above, snapped for the Japanese Disgaea blog).
If you really want a big box of Disgaea stuff, though, you'll want to pre-order from NIS's own store. It'll begin taking pre-orders in July for two different bundles: the same Premium Edition sold elsewhere (with the addition of a bonus soundtrack), and a Super Premium Edition that comes with nine more exclusive toys.
Oh, also, all of these packages include the actual game.