I did the "social studies" stuff (community helpers, cultures of kids around the world, etc.) last year, and we did geography over the summer (he already knew the continents, oceans, states and capitals, but I wanted to teach things like directions, getting from place to place, and things like that). I used Spectrum 3rd grade Geography as a guide, but he's not writing much yet, so I didn't do the entire book the way it's meant to be done. I pulled out the important points for him.
We'll be doing MOH 1 this year. Rumor has it there is plenty of geography in MOH, so geography alone really isn't necessary, BUT it's just my OCD-planning personality that made me want to touch on geography this summer anyway.
I also did a little bit of TX history last year using coloring books sold at the Bob Bullock museum in Austin. We went to the museum a couple of times as well. He knows about some of the major characters in the state's history, and he knows things like the state's icons (bird, flower, fish, etc.), but we didn't dig deep into the details, because IMO, it wouldn't make sense without first doing U.S. history.
In that regard, I also think it makes much more sense to start broad and then dig into the details. I want to see the previews for a movie before watching it, so I also want my kids to do a run-through of MOH before doing anything more detailed like a year of U.S. history or U.S. government. Does that make sense? I always HATED getting bits and pieces of the story when I was in PS. To this day, my knowledge of history stinks! I can't wait to go through MOH a few times with the kids. I like how you're able to do it on the level of the child. It's a very adaptable curriculum.