As well as insurance, which you've got covered, you should also take a valid EHIC (European Health Insurance Card), as most insurance companies expect you to use the services provided free to all EU residents and won't pay for what you could have got free or at reduced price. Yes, I know Greece is in a bad way, including health services, but still important. Make sure you don't use a website which charges you to obtain EHIC, as the NHS one is free.
Personally, I prefer keeping insulin in a cheap stainless steel vaccuum flask, which I had long before I got type 1 diabetes, so was cheaper than buying a Frio pouch, and is cheaper even now to buy a new one than a Frio pouch. As well as being cheaper, a flask protects insulin cartridges against physical knocks, vibration etc. You'll have to fill it with cool water to travel to airport, then empty out water before going through security, then refill with fresh cool tap water once you're through.
As others have said, carry a letter to explain why you need to keep medication, testing kit etc in your hand luggage. Ideally get your hospital consultant or specialist nurse to write one that you can use for this trip and many future ones, as GPs tend to charge up to around ?30 for such a document. Make a few photocopies and keep one permanently with your passport & EHIC, so you don't have to think about it in future.
I'd be more worried about going to a wedding (I hate weddings, due to dressing up and unpredictable food & drink) and giving a speech (haven't had to give a wedding speech) than going to Greece - enjoy your trip 🙂