I love making traditional chicken salad.
Cubed chicken mixed with sundried tomatoes, lots of fresh herbs, garlic, onion, and a light vinaigrette adds something different.
Fresh tomatoes, basil, mozz alone or on some good bread, or you could do bruscetta.
I like the idea of using 'real' meat instead of cold cuts. Cooking some chicken, pork, beef ahead of time and slicing thinly on a tray for sandwiches. I bet it would probably be comparable in cost, if not cheaper...just a bit more work though.
Hummus and a cold cucumber salad makes for a great filling. I just had it for lunch on a wrap. Cube cucumber, dice onion, mashed garlic, dash of olive oil, apple cider vinegar and salt and pepper.
White bean spread made with olive oil, lemon juice, s/p and rosemary (or other fresh herbs).
Tortilla pinwheels with turkey or chicken, sundried tomatoes and pesto OR cream cheese and spinach OR tuna salad with some greens. I made a variety of these at Christmas time and to my surprise, the tuna salad was the hit.
I completely agree with one of the pp about the pulled pork. I made it one year for a party and it was a HUGE hit. Super easy and very cheap. Can easily be done ahead of time too, sometimes is even better after it sits for a while.