I just watched bits of the start of The Impossible Astronaut, few things that I'm sure others have noticed, but here they are regardless. SPOILERS FOR ENTIRE SIXTH SERIES!.
1: He's got the Stetson from Craig, but he's not wearing the coat. Probably because he knows the Doctor Amy/Rory/River have been with doesn't wear it, yet.
2. In the American cafe where they catch up he says he's been running for his life, specifically, he says he's been running for his whole life. This I imagine is what fueled a lot of the Doctor-Ganger theories. The 200 years would have been his whole life if he had been created around the start of this series.
3. After the Doctor is killed, River on the beach fires back, when she runs out of ammo she says to herself 'course not'. This River is the one that's been in jail for killing the Doctor (we assume) and so must know that it's her in the spacesuit and is simply acting surprised for this entire scene. She's already lived out not being shot while in the suit, so when each of her shots misses she says: 'course not'.
4. Old Canton rocks up conveniently, dismissing Amy's suggestion that it might be a clone/duplicate of the Doctor. Opposing my 2nd point. I suppose after something said so bluntly it would be cheap for Moffat to throw a Ganger in.
5. Irrelevant to the speculations, but I just pictured some old bloke turning up to the lake in the morning with his boat missing. "Where's me fucken canoe!"
6. Hmm, younger doctor appears in the cafe, River seems genuinely surprised, slaps him, says it's cold even for him. All this suggests she really didn't know, memory wiped? CONFUSIA.
Think that'll do for now, I might try to piece together a rough River Timeline later, unless someone else wants to do it.