Cody planted a wet one on Miley Saturday morning, and thanked her for whipping up a meal ahead of a swim meet he has today. The pic, which he posted, screams puppy love for the couple ... even though they just went public like 24 hours ago.

We're guessing Miley was scooping up ingredients for Cody's special breakfast when she hit the grocery store Friday evening.

Gotta say, she sure seemed to have a little extra bounce in her step as she left the store with a cart full of goodies.

TMZ broke the story ... the singers were seen smooching and canoodling Thursday while they were at an L.A. restaurant. Miley later joked, "Can a girl not get a f**king acai bowl and a morning make out session in peace?!?!"

As we've reported, they've been friends for years ... but the hookup comes immediately on the heels of Miley breaking things off with Kaitlynn Carter.

BTW ... Miley's already bragged on Cody's bod, especially his abs, and it's easy to see why.

Cody's said he's a member of USC's Trojan Swim Elite team ... and he posted some pics from a practice for this weekend's meet.