@barb1, no need to worry at all!
Never had any problem to bring along testing kits, lancets, syringes, needles, insulin, what have you...
Neither in handbag carry-on or in the checked in luggage. I have not any document either from my GP. Never had one.
Never asked once to show any or been stopped in security control either due to all my diabetes gear in my bag.
I wish actually that there would be less 'hysteria' about this subject. Its a non-issue!
Don't let self-imposed misconceived restrictions limit you life adventure.
Go travel, see, explore and enjoy the world!
With my job I often have multiple flights each week, done so for last 10-15 years.