Hi J.,
OOps. I either sent my answer or erased it half-way through. So here goes again, with my complete thoughts.
I think you have been receiving great responses regarding separation. 99% of the time it is accomplished through the parent demonstrating confidence that preschool is an appropriate choice, just saying "Yes, I am bringing you to school, and I will see you (when). No begging, persuading or cheerleading, as children are fearful when they sense doubt. Same with the food. It is an option, not to be over-discussed.
However 1% of the time separation is not appropriate. If your child is still upset all day long and not enjoying any part of the day, I would examine the situation. Is this child not yet ready? Do you have a mother's intuition that this setting is not a fit for your child? If so, then it is impossible for you to demonstrate confidence you do not feel, your child will sense it, and other options will need to be pursued.
With care, R