Discharge your batteries to 25%. Try to discharge the remote control to 50% or less. Put silicon battery terminal covers on or use electrical tape over the contacts (keep for the return journey or pack some spare). Batteries should be in LiPo bags - look on Amazon, their cheap enough. Don’t leave a battery attached to the drone. Everything in your hand luggage, not checked-in luggage. Customs in England and Spain never batted an eyelid and didn’t bother me at all.