My plan is to add a power-supply unit and a cover for the whole. So first we plan about the power-supply.
For powering the Arduino we add a Li-ion cell. But its voltage its only 3.7V. But we need a 5V supply, so we add a boost converter which make 5V from 3.7V. For the charging the Li-ion cell add an intelligent charger circuit which maintain the Li-ion cell in a good condition. For indicating the battery low voltage condition add an extra circuit to indicate that it need a charging. This is the planning for power-supply section.
Here we only use SMD components for this project. Because we need a small size PCB. Also this SMD work improve your skills. Next is the protective covering.
For protective covering I plan to use plastic name boards. The planed shape is rectangle and make holes for I/O ports and the USB port. Then plan to add some plastic color stickers as art work to improve the beauty.