We took Siera to the beach for the first time over the summer - she was almost 18 months. Umm.. we had lots of sunblock (SPF 35 and SPF 100 - yes, I know, I went overboard

), hats, extra clothing, swimmies, etc. We bought her an inflatable boat, filled it up with water, let the sun heat it for a bit and just sat her in there with beach toys (bucket, shovel, etc.). Hmm what else was a hit... I also kept her under an umbrella most of the time since I was so paranoid of her getting sunburnt.
For the plane ride, we ended up flying around her bedtime so I changed her into her PJs right before we boarded and she hung out for an hour before going to sleep. We had an international flight and they had those baby bassinets in the front row. She slept in there. I recommend taking a cheap umbrella stroller - ours came in handy in the airport.
Oh, and a cool trick I learned for the beach - if you want to take sand off of your baby (ex. legs, butt), rub baby powder over the spot and you can just rub the sand right off.