I only have 2 ways. With pizza and chicken nuggets

Pizza: First get 2 slices of pizza, put them in the main tray, and try to make as stright as possible because "look" is everything. After this pizzas are perfectly alined get a side dish that can be put on sloply(such as corn or fries if you can do it right). Put the food on the edges around the pizza. Then just try to get through the line as quickly as possible. If you lucky then one of the lunch ladies will be buisy talking to somone eles and wont notice you much.

Chicken nuggets: This one is really easy to do. Get in line (mabey at the back so people wont notice you.... or tell on you) get your nuggets in the main tray, then put your extra nuggets in the other trays(dont put more then 3 if you can help it). Next put slopy side dishes ON TOP of the nuggets such as mash potatoes. This will hide the nuggets and the lunch ladies will have to search through the potatoes to find them.

Well there you go. I havent done these myself so results my vary. If anybody tries these and it works tell me okay?