Do i need to enclose the power cable, keyboard, and mouse

No. See the following from Apple Trade In - Apple

Do I have to include accessories like chargers and cables?

No, you do not need to include accessories. If you choose to include any, we will recycle them for you.

You will be instructed not to return your keyboard or mouse. You should return the power cable. If you do not they will reduce your trade in amount by $20, if i remember correctly.