Build an outing into your Vegas visit. Use official visitor information for entrances, conditions and reservations, and make a separate plan for food and supplies.
Red Rock Canyon offers a scenic-drive and outdoor option beyond the city. Check the BLM source for access and current conditions, and arrange your food independently.
Lake Mead is an option for outdoor time southeast of Las Vegas. Use the National Park Service to choose your actual destination and check conditions before a day trip.