I'm assuming you are starting in Chicago but if not then read this in reverse 😉
Chicago has tons of great bars. If you like chicken wings I recommend Jake Melnick's corner tap. For Chicago style pizza try Pizza Uno or Gino's. Loads of hotels in downtown Chicago have rooftop bars.
In Springfield Illinois you have to stop at the Cozy Dog diner. They claim to have invented the corn dog and it's one of those iconic Route 66 stops.
Once you hit Missouri obviously St Louis is your best bet for nightlife.
In Oklahoma, stop at Pops to buy soda from the biggest selection you can imagine. In Oklahoma City there's an area called Bricktown which is basically an entertainment area with load of bars and restaurants.
Once you leave Oklahoma City there are no more big towns or cities until Amarillo, just a series of small towns. Clinton OK has a great BBQ place called Jiggs
Once you hit Texas you'll go through McLean. There's a great cafe where I had breakfast once. I don't remember the name but it's right by the barbed wire museum. There's not much else there!
Amarillo has plenty of bars and place to eat including the Big Texan. Don't miss Cadillac Ranch and bring spray paint. There's a cafe at Adrian TX which is the halfway point of Route 66, imaginatively called the Midpoint Cafe. It was shut when I went so no idea if it's any good!
Next up, New Mexico - Tucumcari is ok for a pit stop but if you want bars and restaurants keep going to Albuquerque, there's plenty going on there. The old town area is nice and you can find great Mexican can food and of course Margaritas!
In Arizona, Flagstaff is a great town with load of bars and restaurants and it's only 99 mins drive to the Grand Canyon from there if you're up for a detour. Williams AZ has fully embraced its R66 status and is full of tacky gift shops but there are also some decent bars and restaurants.
, Seligman and Kingman are R66 must stops. Seligman has the legendary Delgadillo's Snow Cap Drive in. Also stop at Oatman to see the donkeys!
Finally California! Stop at Amboy to see Roy's cafe. You'll recognise it when you see it.
Victorville has Emma Jean's Holland Burger Cafe which has been on TV a few times.
Once you get to Santa Monica you will have tons of options for food, drink and nightlife.
Don't be put off by the outside of places. A lot if the best food in America is served from what looks like a run down shack!
Lastly, have a look at Roadtrippers.com . You can plot your route and it will suggest things to do/see/eat nearby.
Have a great time!