Make the copycat Big Mac sauce first. In a medium bowl, whisk together the mayonnaise, sweet pickle relish, ketchup, yellow mustard, white vinegar, sugar, paprika, garlic powder, and onion powder until smooth. Cover and refrigerate for at least 30 minutes.
Preheat the oven according to the package directions for the French fries and chicken nuggets. Spread the fries in a single layer on one baking sheet and the nuggets on another.
Bake the fries and nuggets until golden and crispy, following the package timing, usually about 18 to 20 minutes. Season the hot fries with salt as soon as they come out of the oven.
While the fries and nuggets bake, divide the ground beef into 8 small patties, each about 2 ounces. Season both sides with salt, black pepper, and garlic powder.
Heat a large skillet or griddle over medium-high heat. Cook the patties for 2 to 3 minutes per side, or until browned and cooked through. Place half a slice of American cheese on each patty during the final minute so it melts.
Toast the slider buns cut-side down in the same skillet for 1 to 2 minutes, or until lightly golden.
Spread Big Mac sauce on both sides of each toasted bun. On the bottom bun, add shredded lettuce, diced onion, chopped pickles, a cheesy beef patty, and the top bun.
Arrange the sliders on a large serving board with hot fries, chicken nuggets, extra pickles, shredded lettuce, ketchup, honey mustard, and the remaining Big Mac sauce.
Serve immediately while the burgers are warm and the fries are crisp. For loaded fries, top a portion of fries with chopped beef patty pieces, pickles, onion, lettuce, and a drizzle of Big Mac sauce.