Welcome to FT!

I've seen Ryanair make people check things because they were too heavy, I've never seen them get the tape measure out, so I doubt you'll run into problems over those extra 3 cm.

Small additional items are OK in my experience.

Watch it at LBC - they've become wise to people offloading their heavy books and laptops onto (non-flying) relatives and friends, and will sometimes do spot checks at the security point using (wait for this!) a set of domestic bathroom scales. Not kidding. That's LBC for you... (one of the most "mickey mouse" aiports I've ever come across - and that's probably an insult to Mickey!)