I've been doing soup in mason jars this fall and winter. I started with a big batch of split pea soup. Since I am the only one who likes it in my house, I portioned it into mason jars and froze it. Then every time I made a soup or stew and had a serving (or two) leftover, I froze it in mason jars. Pretty soon I had 2-3 weeks worth of lunches (and a great wide variety) all ready to go! It is so easy to grab a jar, a spoon, and an apple for my lunch sack. The ONLY complaint/problem is that the soup is sometimes SO frozen that it take a lot of my lunch time to get it heated through. If I know I am working the next day (I work per diem) I will take it from the freezer the night before. If not, sometimes I sneak into the lunch room and let the jar sit in a bowl of warm water for an hour. And I know there are folks who prefer to NOT use a microwave for perceived health reasons. I respect that and I even believe there is some truth behind it.... that said, I am going with a 90/10 healthy life thing right now. And of course, some folks don't have access to a microwave. But I also send soups and stews to school with DS and he doesn't like to use the microwave. I send him in with a thermos that I warm with hot water in the morning before adding the heated food.
I also do overnight oats (usually so that I have a healthy dinner waiting on nights when I get home late) and also make steel cut oats in the crockpot overnight. One batch gives me 4 breakfasts.
Veggies I cut up ahead of time, but fruit I usually only do about 24 hours in advance..... that said, melon lasts a few days after cutting, as so oranges. But apples, berries, not so much.
Instead of always planning lunches and making them ahead, I usually try to make a larger portion for dinners and then pack up the leftovers for the next day (or next two days). This works well with one pot meals especially (soups, stews, chili, stir-fry). Plus my DH works from the home and it is nice to be able to leave him something easy to have for lunch the next day!
Because my DH eats low carb, most of our family meals don't have much in the way of pasta, rice, couscous, or potato. If I make this for the meal, I usually leave it separate so that DS and I can add it as desired (for example, yesterday was ham and white bean soup.... I diced and cooked a small pot of potatoes for DS to add to his portion.... just put a scoop of the potatoes into his bowl and ladled the hot soup over the top!).
Salad greens definitely need to be packed up no more than 24 hours ahead of time (in my experience). Sometimes I cut up all of the salad veggies but pack them up separately and then toss together a salad quickly on the morning it is needed (celery, carrots, and onions can reside well together in a container, but diced tomatoes definitely need their own space!). I try to never pack up something moist (quinoa, pasta, cooked veggies, diced tomatoes) in the greens until it is time to eat....otherwise the greens just get soggy and icky.
FWIW, I ALWAYS pack my meals in reuseable containers. I cringe when I hear people talk about how many ziptop baggies they buy every week to portion their foods. I know washing stuff is a PITA at times, but we need to think about what we are doing to the environment in addition to what we are doing to our bodies. Glass is super easy to wash (by hand or in the dishwasher), doesn't retain strong odors, and can be put in the microwave without fear of chemical leaching. That being said it is heavy to carry around (if you have to walk or take a commuter rail) and of course, can break and takes up a bit more space in the cupboard than tupperware that can be nested. I was so excited to hear you say you portioned your snacks into mason jars!!!
Anyhow.... that's my experience with planning and packing meals ahead! Good luck................P
