Woodfire pizza. It's pretty overdone but it's simple. Make your dough, portion it, get a person to prepare the pizzas and one to fire them. All your prep is straight-forward. It takes like 90 seconds to fire a personal pizza I think. Once you get the timing between two people down, that's it. You just have a simple menu with maybe 3-4 pizzas. 3 staples and 1 seasonal/chef's choice. Vegan/vegetarian, Cheese, and Pepperoni. Then I'd go a little bit more wild with the seasonal one. Try out the more risky combinations and experiments there. Give something for the people who want a twee experience, not just a pizza.

The other one is ramen. People have been doing single-person ramen carts forever. It's just not super common in the states. Do 3 pots of authentic broths. Then prep your condiments. Noodles don't even have to be fresh if you don't want them to, as long as the rest is really good. It's all prep really. Cook your broths in batches. Get up around 8-9am to do other prep stuff. Get everything on the cart/truck. Head out around 11 am to set up somewhere. Then just dish it all out until you run out of food.