To avoid carry-on fees on Frontier Airlines, your best strategy is to strictly use a personal item that fits within the maximum dimensions of 14"H x 18"W x 8"D. Frontier is notoriously strict and often uses sizers at the gate to ensure bags (including handles and wheels) fit perfectly. Many frequent fliers invest in "under-seat" specific bags or backpacks designed to maximize these exact dimensions. Another tip is to wear your bulkiest clothing—like jackets and boots—onto the plane to save space. Some travelers also use the "pillowcase trick," where they stuff soft clothing into a pillowcase, as pillows are often considered a free comfort item rather than luggage. Finally, always purchase any necessary bags at the time of initial booking, as gate fees for non-compliant bags can exceed $100 per segment in 2026.