Yes, on most "full-service" airlines (like Delta, United, or British Airways), you are allowed one cabin bag (overhead bin) and one "personal item" (under the seat), which is often a backpack. However, in 2026, baggage enforcement has become extremely strict, especially on low-cost carriers like Ryanair, Spirit, or easyJet. On these budget airlines, a standard "Basic" fare often only includes a single small personal item; if you bring both a backpack and a rolling cabin bag, you will likely be charged a heavy gate fee (often $60-$100) unless you have pre-paid for the extra bag. For your backpack to count as a "personal item," it must typically fit within dimensions of roughly 17 x 10 x 9 inches (43 x 25 x 22 cm) to ensure it slides completely under the seat in front of you. Always check your specific fare class before arriving at the airport to avoid being flagged by the automated sizers now used at many gates.