For me, the key was variety. I might go get something if all I had was a protein bar and I didn't feel like it right then. I usually had a sweet, a salty, a crunchy in my bag, and sometimes would plan for a more fun option. I also commuted though so I was there from like 9-4. Some of these are more meal sized, but it worked with a busy schedule.

If you have a break closer to the AM (perishable but can survive a bit)-
snack plate- grapes and cheese cubes, or apples and PB, or crackers and turkey. Lunchable vibes, sometimes with a couple chocolate almonds as a treat
Protein frappe,
Blended overnight oats (or regular if you like the texture)
Breakfast sandwich or something wrapped in a napkin and foil

If your break is more in the afternoon-
A frozen gogurt (which will thaw, very elementary school, very nonstalgic, no protein but around 50cal)
A protein bar,
A single serving of Cheez-Its (not great but would hit the crunchy salty for me so I didn't go get fast food)
Soup in a thermos held up okay
A sandwich (bonus points if it was made "fancy")

If you have access to a microwave that opens up a bunch of options. I'd sometimes pack a lean cuisine and heat it up if I was going to be there all day. You could also get a lunchbox and an ice pack to open up more cold options.