This is a very short list because Rice Krispy treats are near-perfect for what they are: The treat with the highest yum:easy ratio on earth.
50% more butter than the recipe says
My personal recipe is a stick of butter and one and a half bags of large marshmallows. This makes them softer and richer. If that half-bag annoys you like it does me then IT SOUNDS LIKE YOU NEED TO MAKE TWO BATCHES.
Fruit Loops
Mostly this just makes them pretty without screwing up the texture or flavor. I do eight cups of Rice Krispies and four cups of Fruit Loops (for you non-Americans that’s … Uh … Ask Siri). And for the love of all things holy use real fruit loops. Not those horrible all natural organic-o’s they have at whole foods.