How about coming over and doing the chores they hate to do but love to have done: clean the gutters, sweep out and organize the garage, winterize the mower, clean the windows, do the cooking.
Maybe just listen to them. Get really interested in their lives and experiences. Ask them to tell you about their first love, their first car, their first memory of their parents/grandparents.
People won’t remember what you got them as much as they remember how you made them feel. Just keep asking yourself what can I do to make my mom/dad feel special now? How can I show my love? How can I show my respect? How can I help?
You’ll have the best holiday ever.