Hey there, welcome! I have 5 kids so I understand. I don't really believe in motivation though. I believe in just doing it whether you're motivated or not. Fake it til you make it?
Filling foods: lots of vegetables. Huge salads. Giant post of veggie-based soups. Baked fish. All can be brought to work in a container. Fruits for snacks. Big glasses of water and mugs of green tea in a thermos.
A big bowl of oatmeal is helpful, too. Bring it in a tupperware and heat it up, or use instant packets.
You can do it