As
@Lucyr mentioned, you do not have to worry about insulin on the flight and travelling unless you intend to put it next to a radiator. Insulin is fine at room temperature for a month. Planes should not get too hot and, provided the insulin is not in direct sunlight, it is fine in your hand luggage travelling to and from the airport.
I recently travelled to Dubai (for work ... not my holiday destination of choice) and forgot to take my Frio wallets. Despite it being 50 degrees outside (it was 39 degrees in the outside bar at midnight), my insulin was fine.
As for putting the insulin in a clear plastic bag, the 100ml limit is on EACH item. You can take more than 100ml of insulin if you want as well as 100ml of shampoo plus 100ml shower gel and 100ml of sunscreen in your hand luggage. Provided it is in a clear plastic bag.
Some airports (e.g. Schipol and Dublin) have bought in new x-ray machines which do not require you to take laptop and liquids out of your bag but this technology has not been rolled out to all airports so I still keep my clear plastic bag in my hand luggage. It is a well travelled bag.
As
@SB2015 suggests, it may be a good idea to avoid hotel fridges - they are not always the most reliable and there have been stories of insulin being frozen. For a normal holiday Frio wallets (or just an air conditioned room) is sufficient.
It is very easy to over think the problems of travel but airports are very used to dealing with people with diabetes with all our little sharp and liquid paraphernalia. Plus, our insulin is pretty robust nowadays.