Dried fruit, lara bars, sunflower seeds, sundried tomatoes, dry couscous, poptop canned chickpeas...
I work full time also, hit the gym five to six days a week for 1.5 hours, take yoga classes, go to a mental health support group, seminars etc. For three years until last May I was also in school but finally graduated. What helps me, because I do not like to eat a lot of processed food and very rarely eat out, is to take my day off and spend an hour or two preparing five or six meals for the work week lunches (and one dinner for Tuesdays since I am gone early morning til late evening that day). I put them in air tight tupperware containers. I make salads, soups (I also have a small thermos), casseroles, fresh fruit and dried fruits portioned, and sometimes make stuff like homemade energy bars (will make a dozen or two at a time and store them in the freezer and grab one each day before heading out when I choose to bring one to work). This week for example I made five portions of a soba noodle and vegetable dish and put it in five small tupperware containers. I snack on brazil nuts and fruits also. I just grab what I need each day then and head out. Sometimes on my day off I also make batches of homemade bread and/or cook up a big batch of dried beans to have on hand for dinner for the week. Anything that is going to take a long time, I do on Sundays. I might also make a huge batch of quinoa or millet and have that on hand for the week as it takes a good while to cook. Sandwiches are a little easier to make on the fly. I know some people at work who keep whole jars of peanut/nut butters at their desk, and one woman even keeps a loaf of bread there lol.
In my desk drawer, for emergencies in case I forget my lunch, I have dates, little single serve raisin boxes, dry oats, pumpkin seeds in a ziplock bag, packets of stevia and cinnamon, tea bags...I always keep a big bottle of water at my desk too.
Edit to add: I carry around a duffel bag with my lunch, purse, gym clothes, yoga gear, work stuff...does get to be a bit much sometimes as I practically live out of that bag lol. But it serves me well.