With ten adults, I'd assume ten people (or fewer, if couples/families) bringing food, so with no further info I'd assume I'm bringing "the salad" rather than "a salad". So I would bring a green salad, because I would want one with BBQ food. If I also brought some kind of composed salad - potato salad, pasta salad, caprese, lentil, etc. - I'd probably bring it in addition to the basic green.
For portability, I'd start with a crunchy lettuce (I like romaine, but something like little gem is also good, or a mix), add any or all of fresh herbs, spiralled carrots (also turnip and parsnip work if you have them), shredded cabbage, sliced radishes, sliced or diced deseeded cucumber, chopped bell peppers, sliced celery, broccoli and cauliflower florets, corn kernels, garbanzo beans.
Fruit, cheese, seeds, nuts, boiled eggs, and mushrooms are also good but perhaps keep them separate if you're not sure about food restrictions or allergies for people to add. I'd also keep olives or pickles separate if there are small children. (Also keep anything non-vegetarian separate.)
Anything wet or mushy I'd also transport separately (tomatos, avocado) and either keep separate next to the main salad or add in just before serving. Dressing(s) on the side, and if you bring croutons also keep those separate so they don't get soggy in transit.
I'd probably make a simple homemade dressing like olive oil-balsamic vinegar-dijon mustard, but also have some kind of generally child-friendly dressing like home-made or store-bought ranch.