Chicken salad? It's pretty easy to make/ pack.
That's pretty much my go to lunch food.
is it healthy/nutritious though?
Yeah it can be if you make it that way. I usually make it with lettuce, cucumber, avocado, fruits (like apples), celery, and grilled chicken. For dressing I use a mix of applecider vinegar and mustard (which is a lot of flavor with really few calories). The only thing the salad is missing is some kind of grain or bread so to make it really a balanced meal you could add a slice of bread or something. Sometimes I mix some rice into the salad.
I buy Lean pockets, frozen steamed veggies (5mins in microwave=freshly steamed effect), baked potato (wash the potato, wrap it up in plastic wrap, put in microwave 5mins=baked potato), Lean cuisines, left overs, home made trail mixes, dehydrated fruits, sliced fresh fruits, and counted out chips or snacks.
In the healthy snacks area, there's nuts (almonds and peanuts tend to be cheaper and better for you than other kinds), cut vegetables (carrots and celery being the most obvious)
In the realm of lunches . . . to be honest I tend to take leftovers from the night before (most anything you make yourself at home is going to be better for you than anything that comes in a box).
Pasta dishes are cool (whole wheat pasta is healthier than white), but store the sauce separately from the pasta until just before you eat it: that way the sauce won't soak into the pasta and make a mushy mess.