After you've completed the Sevii Islands, and beaten the Elite Four a second time, the only thing to do is to catch Pokemon and complete the Pokedex. The special tickets can get you some very rare Pokemon, however, you can only get them at certain events (ex. Pokemon Rocks America) The tickets will take you to Navel Rock or Birth Island, depending the ticket. When you get to Navel Rock Island, you can catch Lugia and Ho-oh at Lv. 70. On Birth Island you have to solve a puzzle to unlock Deoxys, which is at Lv. 30. Also in Pokemon Emerald, if you get the Old Sea Chart, you can catch Mew, which is at Lv. 30. If you don't go to the events, then you can use an Action Replay, GameShark, or CodeBreaker to get these items.