If
Double Dragon Energy worked for Rayquaza that would be a dream come true, but unfortunately like
@TatsuyaOrimuta said, it needs
basic energies in order to gain the benefits of extra damage.
Max Elixir is definitley a card you would use for it for any version of Expanded Rayquaza since you're running a bunch of basic energies specifically for the ability anyway, so getting that near-guarantee on a Rayquaza is pure gold. Past this paragraph is research I see on the internet.
Trainer's Mail If Rayquaza ever needed more item speed has that as an option to grab anything like a Mysterious Treasure or Acro Bike or really anything to help speed through your deck and set up Rayquaza super early.
Friend Ball if your opponent ever plays the same kind of deck is there, and while we don't have that fancy new
Shuckle we're going to get in the next set, we have the original Foolish Burial of the Pokemon TCG that being
Battle Compressor to not only send Supporters to the discard pile for VS Seeker, but basic energies as well for Rayquaza's ability.
These next couple of cards are all basic dragon pokemon that look a little interesting to me.
Dragonite-EX (Furious Fists) is another option. Sure you do have Koko which essentially does the dame thing except more damage, but the benefit to running Dragonite is he's searchable via Mysterious Treasure and if you needed another basic dragon pokemon to set up with Latias Prism Star, then he can act like one in a world with not a lot of good basic dragon pokemon.
Flygon-EX (I guess?) Might be a decent little tech for forcing a switch for specific needs. And it's another basic dragon pokemon which is good for the reasons stated above. Not really too good for anything else so maybe not him but it's an option nonetheless.
Hydreigon-EX (Roaring Skies) Can provide better retreat cost if you play stadiums (
Skynarrow Bridge for complete free retreat maybe?) incase your Rayquaza's need that flexibility for once again specific reasons. There's also
Latias-EX (Plasma Freeze) which can provide as a wall for pokemon using special energies.
If Rayquaza was ever a deck in Expanded, I don't think his playstyle would change too much, it looks to me that he has tools that make a positive yet minuscule effect on what he does. I just think he needs to have a solution for decks that can block his abilities or damage, or not be so item-heavy against decks like Seismitoad.