KLIA2 is a really huge airport with a shopping complex attached to the airport. Compared to KLIA, there many places to sight see and shop that one would not feel too bored (especially if one need to wait sometime before can check in).
In the past, I have always thought that eating at the airport is very expensive. There are many places to eat in KLIA2 like KFC, Old Town, Starbucks and Hometown Coffee (that is before you enter the security check-in). But if you wish to have variety and more reasonably priced food, then I would suggest the Rasa Food Court at level 2M (you can refer to KLIA2 website for further info). It is located at the same floor of the Plaza Premium lounge.
In the food court, there are mamak, Chinese, Thai, Malay and Western dishes. The prices are of course more expensive compared to eating in town but it is not really too expensive. For example, their teh tarik (an extra large cup) cost RM4.90 and claypot chicken rice cost RM8.50 or RM9.50. I got a set of local curry puff (karipap) with teh tarik for RM4.90 and a Western meal for RM12+ (it was on offer- their normal price is usually around RM15- RM20+).
Usually, when I get to the airport, I would always check-in my luggage first (make sure everything is okay) before going for my meals. I only learned about the food court recently when I send a few friends to the airport.
After you enter the Immigration checkpoint, the choices would be lesser and the food would b expensive.