The clauses that cause the most trouble
Final headcount. Set a date for the final count and say what you charge if more guests show up than were confirmed.
Site access. A truck that can't get to the spot, or parks on a slope, can't serve. Spell out level ground, the route in, the distance to power and water, and who gets any permit the venue needs.
Cancellation. Write the terms as dates and amounts, not "reasonable notice". The client should know exactly what they get back at each point.
Minimums. For public events where guests pay you, say what the host owes if sales fall below the minimum. To set that number, run the event through the food truck event calculator and start from its total costs and break-even.
Catering contract vs event vendor agreement
A catering contract is for private events where the client pays you for the food: weddings, office lunches, parties. An event vendor agreement is for festivals, breweries and markets where the public buys from you and the host charges a fee or a percentage of sales. They cover different risks, so keep both on hand.
Taking deposits
Send a deposit invoice with the contract and hold the date only when it's paid. Note the deposit amount, due date and balance on the invoice, and keep copies with the signed contract. Before quoting, check your food cost with the menu pricing calculator so the per-person price covers food, packaging and labor.