Good advice from Gduffy, that's a good place to start.
Your friend will also need , if he doesn't have it set up in advance, he will find it very difficult to get a pitch at festivals, markets etc.
If he's planning to cater at large festivals, he will need to approach the organisers asap as these events have a limited number of pitches and are well subscribed.
He should also think about restricting himself and his equipment to only hog roasting. If there was, for example, another swine flu outbreak or some scandal affecting the pork industry, his business would be severely affected. Better to have equipment with which he can offer a range of food items.