The $100 Hamburger is nothing more than an excuse for pilots to go flying. It is called this because flying to another airport buying lunch and flying back, can cost quite a bit in fuel, or airplane rental. The actual lunch is of little importance, the whole reason is to get in an airplane and go somewhere. It has something to do with the freedom to get up and go to another destination and do so in an unconventional way. The novelty has not worn off for me yet.
Fortunately (or unfortunately, depends on how you take it), I live near the airport in Greeley, CO that has good hamburgers, so my $100 hamburger is more like a $6.34 burger. Flying before or after is optional for me. The Barnstormer restaurant is in the main terminal building with a good view of aircraft taking off and landing on runway 9/27. They serve both beef and bison burgers among other comfort food, so this is a fairly popular destination for hungry pilots.
www.100dollarhamburger.com is a good place to look if you are interested in finding restaurants at general aviation airports.
Lunch trips like this usually include lots of good conversation. Taking your spouse or friends who are interested in general aviation also helps out as most of the conversation will likely be around flying, etc. They will also get as much enjoyment out of the flight as you will.