Hungry campers won't be able to wait to get their hands on this foil-packet dinner.
Heat campfire or grill to medium over direct heat. Combine butter and parsley in a bowl. Season with salt and pepper. Chill until ready to use.
Tear two 12x20-inch pieces aluminum foil; overlap pieces slightly. Place carrots, potatoes, garlic, cumin, and thyme in center of foil. Drizzle with oil and season with salt and pepper. Fold edges of foil up and over to create a packet; pinch edges to seal. Grill, turning packet occasionally, until potatoes and carrots are tender, 28 to 30 minutes. Open packet and drizzle with vinegar.
Meanwhile, season steaks with salt and pepper. Grill, turning occasionally, until the internal temperature on an instant-read thermometer is 120°F to 125°F (for medium rare), 8 to 10 minutes per side. Transfer to a cutting board and top with butter. Let rest 5 minutes before slicing.
Serve steak alongside vegetables.