I'm gone 12 hours most days between class and work, so I invested in a 4-cup leakproof Pyrex container. I wake up pretty early, so sometimes I make separate things to pack for lunch, but a lot of days it's leftovers from dinner the night before. Having a real meal in the middle of a busy day is sometimes my saving grace, even if I'm eating in class. I'm also really into breakfast, but it's not for everyone. Lara bars are technically primal if you really want a bar, but they don't fill me up at all and I only eat them occasionally as a treat.
You need 30 minutes to make and eat an omelette with cheese and bacon and it will pretty much fill you up for most of your shoolday