The Old Man really loves Star Wars and was disappointed that he couldn't make a deal on a commercial R2D2 cooler stating if he couldn't sell it he's take it home and put it on his porch.
Rick loves anything to do with history and bought an Incunable book (a book made during the first 50 years of the printing press) and decides to keep it for himself. Though Corey and The Old Man make him buy it at full price, more than twice of what he paid for it.
Chumlee is an All around geek being into the usual stuff like video games and toys.
Writer Revolt: Rick and Corey's fighting in Season 2 was artificial scripting caused by Executive Meddling. After the bitterness started seeping over to real life, Rick told the History Channel to stop it or they'll end the show/take it to another network, and they listened. This incident is referenced in the new version of the opening, where Rick mentions family being more important than business.