I managed to get a 145cm, 15kg load capacity, aluminium, tripod into a 40x30x20 cm underseat cabin bag.

Everything I managed to cram in and get through security with zero hitches.

https://i.imgur.com/toZ9NxR.jpeg

Edit: Ok I had to take the tripod apart but I am still quite pleased with myself and thought it would be of use to others.

Edit II: For anyone unfamiliar with European budget airlines, large cabin bags and hold bags cost extra and have weight limits. Hold bag is pay more get more and the paid cabin bag is limited to 10 kg.

However, the underseat cabin bag is free with no weight limits. I flew "Vueling" who seem to have the smallest allowances.