Spoilers. Highlight to see.
Yeah. That part at Denny's was definitely another flash-forward. The only thing we don't know is whether he's running from something, or to it. It could go either way. You may remember in the pilot when he's standing in the middle of the road waiting for sirens with a pistol, it turns out that the sirens are coming from fire trucks. If he's running from something, it could either be Hank or Jesse/Mike.
Hank: obvious enough. He's been after Walt since day one. Now that he has the DEA believing in him, he may have the man power to find out Heisenberg's identity. The loophole with this outcome, though, is that Jesse was absent. If this is the case, Jesse is either dead, arrested, or running the show without him.
If Jesse's following him, it could be because he finds out what happened with Brock and the ricin. He's already shown that he's willing to kill Walt over that (he almost did). The both of them are going to NEED Mike's help to get their operation started. Mike hates Walt, Jesse and Mike trust each other. It's possible that the two of them turned on him. Now, the issue with this is that Walt somehow arranged to have a guy drop off a duffle bag incognito. It sounds like something Mike could have arranged, so Mike is probably still on his side at this point.
Let me also say that this could be a scene from the NEXT season. Season 6. This was going to be the end of Breaking Bad, but they split it into 2 seasons. If either of the two above scenarios come true, there may not be a full season of content left in the show. For this reason, I'm leaning more towards Walt is going somewhere to get someone or the scene is showing something much further down the road. After all, he coughed in the bathroom which could mean his cancer is coming back. Either way, Walt has to die at the end of the show and Hank has been a sleeping threat the entire time. That can't play out until the end of the show regardless, which means Walt has to stay successful for at least this season. If I'm wrong and Hank is on his trail and it's happening in season 5, then Walt is going to kill him.