I would just toss them with enough bacon grease to make them shine.
At this time of year I like to plump/poach a few craisins in melted butter and add them to the green beans for a little color.
At other times a few slivered almonds, sliced mushrooms, chopped onions, minced garlic cloves, diced red bell pepper or hot red pepper flakes can give the green beans a lift. I usually sweat the additional ingredient in some melted butter or olive oil to soften before adding the cooked green beans.
The leftovers can be used as a simple salad if you toss them with a little fresh lemon juice, red wine vinegar, apple cider vinegar and some olive oil or you can go all out and make a musgo version of a salad niçoise, don't get hung up on the recipe just use what you have on hand.
Leftover Green Bean Niçoise Recipe | MyRecipes.com