Potion. Continue down, where some lower-level employees from Shinra will attempt to corner you. Fight them if you want experience, but you can keep running away. Eventually, Cloud breaks away with a well-timed escape.You start in an enclosed area. Jessie sets off a bomb, then you run away and split up, planning to meet at the Sector 8 station. You can now go up the stairs, and there you find the flower girl from before, who you can have a short conversation with. This affects a future event, you can enable spoilers for details.
Go down and below the first large, circular area. Near a small rectangular object, you'll find a Potion. Continue down, where some lower-level employees from Shinra will attempt to corner you. Fight them if you want experience, but you can keep running away. Eventually, Cloud breaks away with a well-timed escape.
Follow your crew in the train, then talk to Barret, then Jessie. She shows you the Midgar Rail system, and explains what they're doing. Talk to her again, then go talk to Barret. Next stop is Sector 7, and Barret tells you to meet back at the hideout. Go left and up to find your save point. Don't talk to the person standing near it unless you want to spend some time reading.