In many cases catering pitches are charged at a higher rate than a standard table. This tends to be because of the much higher potential for selling food and drink. Because of this potential it can be very competitive.
You will need to think about the volume you can sell at any particular pitch. It is a good idea if you can to research pitches for the volume of passing trade during recognised meal times and to look at competition. Do not be afraid to ask people the question, -If we had a catering van here, would you purchase? What food would you like?
You will need to make sure you have all required licenses like hygiene or alcohol.
Catering is big business and people always need food.