I, agree with hou_ge2000, before buying the paints check the kit instructions. This is to avoid having to buy paints that you may not need at the moment.
The list provided by shermanfreak is a good guide too.
I am still a beginner in the hobby but I have been into painting for a long time (watercolor, oil, acrylics, pastels, etc.) and these are some tips that I can share based on my experience:
1.) Buy enamel paints for metallic colors (gun metal, chrome silver, flat aluminum, metallic grey, etc.) These colors are often used for minor details only and they always last more than one kit. Acrylic Paints tend to solidfy and become hard over time making them difficult to apply in thin layers with good color quality. Enamels are easily thinned while retaining their color.
2.) If you need only a small amount of some colors for minor details, try mixing your own. This could probably save you a lot of money.
3.) For large areas, use acrylics. For almost the same price, acrylics come in a larger bottle than enamels. Acrylics when applied properly also dry up faster than most enamels.
Happy painting!