Tell us where you're going, when, for how long, which airline you're flying and the size of your bag. We build a packing list from real monthly climate and your airline's carry-on limit — then tell you whether it fits in the cabin, by weight and size.
About the data: monthly climate normals (mean daily high and average rainy days) are real, from Wikipedia climate tables citing national meteorological services. Carry-on weight limits and dimensions come from each airline's published baggage policy (Ryanair 10 kg, easyJet 15 kg, Wizz Air 10 kg, KLM 12 kg, Lufthansa 8 kg, Vueling 10 kg, Transavia 10 kg, Aer Lingus 10 kg, Iberia 10 kg, TAP Air Portugal 8 kg, SAS 8 kg, Air France 12 kg). Item weights and bag-size presets are illustrative estimates — a packed bag also weighs ~2.5 kg empty, which is included in the total. The verdict only says "fits carry-on" when both your bag's weight and its dimensions pass your airline's allowance; if you haven't chosen a bag size it's marked as not checked rather than assumed to fit. Weather suggestions are rules of thumb (e.g. an umbrella when rain falls on more than ~40% of days); always check the actual forecast before you go.