What Can I Feed A Kitten Besides Cat Food?

My kitten is only 2 weeks old, but i want to start feeding him kitten milk replacer (or what the name of it is). I found some at petsmart. The bottle says that it needs warm water and not hot water. What does that mean? Does it need to be warmed before using or something? Also, he gets very little food; 1-2 times a day. I noticed his eyes are getting baggy like they would if he was starving…He also started getting hairballs in his vomit now too….