How about yummy, quick deli-style dips/filling you can make the night before? People can eat them as is, on sliced baguette bread etc.
Here's a few quick but yummy dips...
Coronation Chicken
Mayo, medium madras curry powder, honey, sultanas or raisins, cold chicken (cooked), mix together to taste, being careful with the honey!
Waldorf style salad
Chopped apples, grapes, celery & cheese mixed with mayo.
Prawn Marie Rose
Mayo (80%), tomato ketchup (20%) ish. Mix together with a squeese of lemon juice and add cooked prawns.
Yummy, quick bread things.
Slice a baguette or two up slightly diagnolally and spread pesto sauce, some mozzerella, and a slice of tomato. Stick in the oven and yummy hot or cold.
I cooked all these things up and more for a party last week. Did the dips the night before and the bread the nest day. Very quick, very nice looking and very yummy IMO of course.
Good luck and I hope this helps.