Go find or buy some TMs first. Machop probably won't help much at all, but Absol should be able to learn moves like Shock Wave and Ice Beam. Pikachu should have a powerful Electric attack, since Rayquaza is Dragon and Flying. Maybe go in more Dungeons first to level up your team some more. Try getting some moves for Absol and Pikachu, too. Let me know if this works at all. It'll still probably take a couple of tries to beat Rayquaza, so don't get frustrated and make the best of each turn powering up, maybe using something to Paralyze or Poison Rayquaza, and use the strongest moves you have.