What do astronauts do while traveling to the ISS so they don't get bored? I know they must check equipment and do science experiments, but what they do in their free time?
It depends somewhat. There are basically 2 profiles to getting to the ISS. One of them requires only 6 hours to dock with the station, in which case there is no down time at all. As for the longer, 2 day docking profiles, they most likely don't hit that point. There is a lot to do in those two days, and much like driving across country, there's a lot to see to prevent that boredom from sinking in completely. Early flights were in fact very operator intensive, so there probably wasn't much time to be bored. They do have access to television, but I can't find much more in the ways of entertainment prior to docking with the space station.
I've asked a couple of astronauts, and apparently they actually do get surprisingly bored! (This is in the context of long-duration missions on the ISS, not transfer from/to Earth on Soyuz). They have limited, slow internet access, a library of DVDs and iPads, as well as whatever books they can bring in their Personal Preference Kits (1kg max). I haven't seen any references to whether Kindles have been approved for flight.
There are some musical instruments on the station including a guitar and a keyboard. Photography is also a popular pastime. Suitably licensed astronauts can chat to hams on Earth via amateur radio.