I pack lunch for my first grade DD everyday & it's a rotating list of things that she likes. I include a freezer ice pack & I bought a good sized lunch box with shoulder straps from Target, I think it is a thermos brand. I find most boxes to be way to small. It usually contains a main sandwich type thing weather it is PB & banana or with strawberries or jam, tuna salad, egg salad, a bagel with cream cheese, pitas & hummus, curry chicken salad, a hummus veggie wrap. I also include a snack to be eaten in the classroom early in the day that is usually either a fruit salad, an apple, cut up veggies with hummus, yogurt sometimes with granola, sometimes not, applesauce, berries or cheese & crackers. I add her SS thermos of water. Then depending on what I've already packed I might add carrot sticks, more fruit, cheese, yogurt, coleslaw, a homemade date bar or granola bar, apple sauce, cheese & crackers. She eats another snack as soon as she gets home from school. Then dinner is her last meal.
My older dd gets lots of leftover soups, & bean burrito type things, & adores hummus veggie wraps as she is eating more towards vegetatrian these days. She loves nuts & veggie burgers & doesn't care for the mayo type sandwiches so much. Whereas my LO isn't into hot food at lunch time & adores anything with mayo! To keep food hot get a SS thermos fill it with boiling water in the am while you heat up the soup or whatever, then dump it out fill iwth soup & it stays hot for a long time!
Just go with what you know she likes. About containers we were nearly plastic free, but the schools do not allow glass containers where I am so I bought lock & lock containers instead of wasteing lots of zip bags.
Giving Love serves as a wonderful reminder that we already have an abundance of Love within, "it is in giving that we receive."