Just two days after he touched down in Florida to begin his new career in the MLS ... Messi evidently needed some food for his crib so badly, the $600 million man took it upon himself to hit up a local supermarket to nab some groceries.

The 36-year-old soccer G.O.A.T. pushed his own cart and traversed through some gawking fans to make the run ... and at the end of it all, he walked away with what appeared to be several boxes of sugary breakfast treats.

The footballer, though, seemed to have a relatively easy time being out in public ... while he did pose for a selfie with at least one fan at the store, most seemed to let him go about his business without bothering him.

Of course, that's a stark contrast from his usual norm in Argentina ... where most of his nights out involve being swarmed by hundreds of fans.

But, Messi is still getting the VIP treatment, at least in some parts of his new home ... while out at a dinner earlier this week, he had to deal with several people who had lined up to get a glimpse of him on his way to his car.

Messi is slated to be formally introduced by Inter Miami on Sunday ... so it might be another few days before the mania around the soccer player really kicks off in South Beach.