"Priority & 2 Cabin Bags" is a specific baggage and boarding tier popularized by European budget airlines like Ryanair. When you purchase this add-on, it grants you two primary benefits: first, you get to enter the Priority Boarding queue at the gate, allowing you to get onto the plane and settle in before the majority of passengers. Second, and perhaps more importantly, it increases your luggage allowance. Instead of just bringing one small "personal item" (like a small backpack that fits under the seat), you are permitted to bring two bags into the cabin: the small personal item plus a 10kg wheelie bag (usually 55x40x20cm) that fits in the overhead locker. Without this specific add-on, most budget airlines will force you to check your larger carry-on bag at the gate for a steep fee if the overhead bins are full. For many travelers, this is the most popular upgrade because it saves time at the destination by avoiding the baggage carousel and ensures that your valuable or fragile items stay with you in the cabin rather than being stowed in the aircraft's hold.