My hypo snacks are not liquid so I have not had to deal with the issue of carrying them through security.
They never bat an eyelid at my GlucoTabs or muesli bars.
A letter from your DSN or consultant or doctor is recommended for travel. This should be written in a way that can be used again and again. Most GPS charge for this whereas most diabetes clinics don’t. In twenty years of travelling on hundreds of flights (I am not exaggerating), I have needed my letter once. So, don’t panic if you don’t have one. In most cases a copy of your repeat prescription is a good enough alternative.
in fact, most security crews pay not attention to any diabetes kit. Including Libre - the needles are too small to show up on the x-ray. You may want to put your spare insulin in a clear bag with you toiletries. Some security guys don’t care, others need to make themselves “useful”.
Some people prefer to tell the staff they have diabetes. I don’t bother. Security don’t care and nor do air crew.
In the olden days when you used to have to check in in person, I did enjoy answering the question about whether I had any sharp items in my hand luggage. I would say “yes” but offer no explanation until the airline staff had started to show concern. Then I would add “I have diabetes” and see them visibly relax.
Take all your diabetes kit in your hand luggage and, as
@Saoirse mentioned, take twice as much as you think you will need. Some people request a separate medical bag. I have never needed this and always prefer the minimum number of bags.
There are two reasons for keeping your kit with you rather than putting it in the hold - you cannot guarantee the temperature in the hold and hold luggage may not arrive at the same time as you.
If you put your hand luggage in the overhead locker, make sure you keep your hypo treatment out. From personal experience, I can tell you it is not pleasant having a hypo whilst taking off and having to endure the air crews’ stares and stern words when you jump up to get your dextrose out.
