When going to the beach for the day, I prefer to keep insulin in a ziplock bag set inside a cooler along with the drinks. I do the same with my meter, supplies, and Epipen, but they're in an insulated carrier (and also in a ziplock bag) so they don't get
too cold. I try to sit pretty close to a life-guard post/station, and have never received any hassle about injecting in public. Most of the people there are pretty wrapped up in what they're doing (sun-bathing, swimming) and never even notice. Those who do, don't usually have a negative reaction, but are just curious.
Since I'm usually slimed up with oil and/or lotion, I use an alcohol wipe for my fingers to test. The same goes for the injection spot.
The days that I go to the beach for only a couple of hours, and my bgl has been stable for a few days, I don't carry my insulin with me. Just the meter and Epipen. (We only live 5 min. away if there's a problem.) I know...

(preparing to get clobbered for this behavior). I sit even closer to the life-gaurd station on those days "just in case," even though my bf is always with me. My most common prob when at the beach is going low.