IMO a 50mm-200mm focal length lens is going to be better for a photo shoot (with a large aperture for the bokeh [background blur] and it is faster by allowing more light in letting you use faster shutter speeds), but for food shots you'd want somewhere between 35-50mm, the best length IMO is 50. It is perfect for almost everything. If you are going to go and get a 50mm lens though you are going to want a fast one (large aperture). So I would just go for a 50 f/1.4. If you are on a budget, however, go for a 50 f/1.8.
Here is also a read on the difference between FF and a crop sensor.
Now if you want to buy a 50mm lens it is going to be equivalent to about an 85mm lens, so you should take that into account when buying a lens for a crop body. But to be honest I wouldn't even worry just go with a 50 and don't think about it. You wont regret it
Btw, what camera do you have?