I have an espresso truck and my home county, Chester, PA, has a very strict and thorough Health Department. My certification from them is only good in Chester, so I also acquired the PA Dept of Agriculture permit for a Mobile Food Unit. This is a statewide license unless a local municipality has their own requirements, then you must satisfy those for them. Compared to the drill I started with in Chester County, I am amazed that when I go to festivals in more rural settings, I never see any kind of inspection, though that would not exempt one from satisfying the requirement to be licensed by someone. I doubt there is anyplace in the country where you can prepare and serve food without some kind of permit, whether a particular region has the manpower to enforce it or not.
I went to Florida for a month to try out Spring Break, and found the licensing very confusing, almost impossible to get what you need off the web, seemingly redundant agencies misdirecting me, etc. I think the most accessible regulations are on the west coast, because when I search regulatory issues I often find myself bookmarking something on mobile vending from Oregon, Washington, or California. There were family and other reasons I went to Florida, and probably won't do it again, at least commerically. I plan to get permits in nearby states - NJ, DE, NY, MD, WV - but this is my start up year and I'm taking it slow. My main interest is music and alternative cultural events, so I am usually looking for multi-day events where it pays to travel, even if I end up camping next to the truck, which happens. This is a personality thing - I have absolutely no interest in a fixed location or route.
I start early in the winter looking for bookings for the coming year - early spring events will likely be filled by mid-winter - but often festivals are run by volunteers who change from year to year, and sometimes they have last year's website still up until a couple months before the event. I've applied to things and had to assume they weren't interested because I got no response, only to have them call me 2-3 months later when they start working on it. What it comes down to is that you are always looking for places to go to.
By the way, your Safe Serve is recognized nationally, and if a region has regulations, it will accept Safe Serve for food handling. Most regulations are pretty uniform, but I've heard of quirky contradictions - a truck like mine had some problems getting licensed because they didn't have a category for it. It wasn't a Mobile Food Unit to them because it didn't have a 3 basin sink and a grill. So they had to call it a cart, even though it was a truck. However, they had a reg that said you couldn't have a blender on a cart. The person couldn't get it through the review with a blender, and had to accept not being able to make iced coffees and smoothies if they wanted to work there. This kind of failure of the imagination is typical of bureaucracy, but I find most health departments very human and professional, and if they know you are trying to do the right thing, they tend to relax and be helpful. Obviously, there are many vendors trying to get away with whatever they can, and that's a bummer for the rest of us, because it just creates embattled, skeptical inspectors.
I hope others will submit to this thread. Good luck, Laura.