If you bring lunch to work or school from home, it's called "packing" your lunch. Technically, "packing" a lunch means wrapping it and putting it in a bag or box:
My mom used to pack my lunch for me every day.
But even if someone else actually made the food for you and put it in your bag or lunch box, it's still OK to say that you "packed a lunch":
I packed a lunch today, so I'm just going to eat at my desk.