My youngest daughter Olivia loves salads so she often takes one for lunch. Here's how we do it:
On the bottom of a medium size Gladware container we put some Feta cheese and a protein (usually some turkey or ham lunch meat sliced up or some leftover grilled chicken and some bacon pieces.) Next we put the lettuce and other crunchy veggies on top (she likes red onions, cucumbers and carrots). If she wants a hard boiled egg we slice it up and put it in a snack size Ziploc bag to contain the smell. Another Ziploc can hold wet veggies like black olives or roasted red peppers. These bags get thrown in on top of the lettuce. Finally a small container of dressing goes in. It all gets sealed up inside the Gladware, if the dressing pops open no problem.
This can easily be done the night before and kept in the fridge over night. In order to prep a few days in advance you can clean a couple of hearts of romaine and have it cut up and ready to use. Or buy pre-washed salad greens at the store. You can also boil several hard boiled eggs and keep them in the fridge for up to 5 days. When you clean and cut up a cucumber you can save the extra for the next few salads.
The only other thing she needs to pack is a drink, a dessert and of course a fork and napkin. When lunch time rolls around she put all the components together, puts the lid back on, shakes it up to combine and Viola! She has a gourmet salad for lunch!