Hi, I’ve never flown to Kalymnos yet (I arrive 29/5/24) but I have flown with climbing gear in the US and to Greece. I’ve flown with sport climbing gear and trad gear in a carry-on with no trouble. The only thing they will not let you have in a carry-on is a nut tool (and a knife or piton hammer, obviously). I pack my carry-on with my essential (hard/expensive to replace) gear for climbing, assuming that if the airline looses my bag, at least I can buy a rope and helmet and get still enjoy the trip.