This is what i have been using for quick invoices, not really a contract, but an agreement for lawn mainteancne.
Its not perfect but its a 3 part carbon copy. White, pink, and yellow. I give the yellow one to the customer, pink one goes in our records for a work order, and white is filed. After the job order is completed we will mark with a time stamp, on it, completed and put it in our, completed(but not paid pile).... A formal invoice is sent out to the customer via quickbooks and then once they pay we will file away under paid jobs and mark the invoice paid on quickbooks and our pink copy.
We put the terms of service, payment information and the customer signature in the (TERMS) space provided.
This ensures us if quickbooks ever fails, we have a backup and the original to look at.
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