If you are in the Saphan Kwai area close to the BTS Saphan Khwai Station then the well-known Beer Park makes for an excellent stop-over. Its a short taxi-ride from the BTS Kampaengphet Station but well worth the effort. The bar is mainly middle class Thai and from time to time you might find the odd expat there.
The Beer Park has very friendly staff and the bar is well managed. The food is good no tourist prices like in Silom at this bar. If you want to sit back while in Thailand with the locals then this is an excellent bar for that. The fried chicken salad with crispy morning glory lemon chicken cream dip is excellent, so try that while you are there. Its a bit off the beaten track for foreigners but a good introduction to life in Thailand. The live band is also not bad and makes for a good backdrop while eating.